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Global modifier genes influence the mapping of genotypes onto phenotypes and fitness through their epistatic interactions with genetic variants on a massive scale. The first such factor to be identified, Hsp90, is a highly conserved molecular chaperone that plays a central role in protein homeostasis. Hsp90 is a "hub of hubs" that chaperones proteins engaged in many key cellular and developmental regulatory networks. These clients, which are enriched in kinases, transcription factors, and E3 ubiquitin ligases, drive diverse cellular functions and are themselves highly connected. By contrast to many other hub proteins, the abundance and activity of Hsp90 changes substantially in response to shifting environmental conditions. As a result, Hsp90 modifies the functional impact of many genetic variants simultaneously in a manner that depends on environmental stress. Studies in diverse organisms suggest that this coupling between Hsp90 function and challenging environments exerts a substantial impact on what parts of the genome are visible to natural selection, expanding adaptive opportunities when most needed. In this Perspective, we explore the multifaceted role of Hsp90 as global modifier of the genotype-phenotype-fitness map as well as its implications for evolution in nature and the clinic., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Despite abundant genomic and phenotypic data across individuals and environments, the functional impact of most mutations on phenotype remains unclear. Here, we bridge this gap by linking genome to proteome in 800 meiotic progeny from an intercross between two closely related Saccharomyces cerevisiae isolates adapted to distinct niches. Modest genetic distance between the parents generated remarkable proteomic diversity that was amplified in the progeny and captured by 6,476 genotype-protein associations, over 1,600 of which we resolved to single variants. Proteomic adaptation emerged through the combined action of numerous cis - and trans -regulatory mutations, a regulatory architecture that was conserved across the species. Notably, trans -regulatory variants often arose in proteins not traditionally associated with gene regulation, such as enzymes. Moreover, the proteomic consequences of mutations predicted fitness under various stresses. Our study demonstrates that the collective action of natural genetic variants drives dramatic proteome diversification, with molecular consequences that forecast phenotypic outcomes., Highlights: - Proteome diversity arises from natural genetic variants, with divergent proteomes in closely related parents and progeny. - Cis- regulatory elements had strong individual impacts, but coherent trans effects combined to dominate protein expression. - Directional selection and frequent transgression suggest much of the proteome is under selective pressure. - Many trans -regulators are enzymes or transporters, with fewer than 4% of pQTLs linking known interactors. - Genome-to-proteome connections predicted the fitness impact of mutations under various stresses, including a strong but hidden causal variant in IRA2/ NF1.

Cell size is tightly controlled in healthy tissues and single-celled organisms, but it remains unclear how cell size influences physiology. Increasing cell size was recently shown to remodel the proteomes of cultured human cells, demonstrating that large and small cells of the same type can be compositionally different. In the present study, we utilize the natural heterogeneity of hepatocyte ploidy and yeast genetics to establish that the ploidy-to-cell size ratio is a highly conserved determinant of proteome composition. In both mammalian and yeast cells, genome dilution by cell growth elicits a starvation-like phenotype, suggesting that growth in large cells is restricted by genome concentration in a manner that mimics a limiting nutrient. Moreover, genome dilution explains some proteomic changes ascribed to yeast aging. Overall, our data indicate that genome concentration drives changes in cell composition independently of external environmental cues., (© 2024. The Author(s), under exclusive licence to Springer Nature America, Inc.)

Protein aggregation is a hallmark of age-related neurodegeneration. Yet, aggregation during normal aging and in tissues other than the brain is poorly understood. Here, we leverage the African turquoise killifish to systematically profile protein aggregates in seven tissues of an aging vertebrate. Age-dependent aggregation is strikingly tissue specific and not simply driven by protein expression differences. Experimental interrogation in killifish and yeast, combined with machine learning, indicates that this specificity is linked to protein-autonomous biophysical features and tissue-selective alterations in protein quality control. Co-aggregation of protein quality control machinery during aging may further reduce proteostasis capacity, exacerbating aggregate burden. A segmental progeria model with accelerated aging in specific tissues exhibits selectively increased aggregation in these same tissues. Intriguingly, many age-related protein aggregates arise in wild-type proteins that, when mutated, drive human diseases. Our data chart a comprehensive landscape of protein aggregation during vertebrate aging and identify strong, tissue-specific associations with dysfunction and disease., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Protein aggregation, which can sometimes spread in a prion-like manner, is a hallmark of neurodegenerative diseases. However, whether prion-like aggregates form during normal brain aging remains unknown. Here, we use quantitative proteomics in the African turquoise killifish to identify protein aggregates that accumulate in old vertebrate brains. These aggregates are enriched for prion-like RNA-binding proteins, notably the ATP-dependent RNA helicase DDX5. We validate that DDX5 forms aggregate-like puncta in the brains of old killifish and mice. Interestingly, DDX5's prion-like domain allows these aggregates to propagate across many generations in yeast. In vitro, DDX5 phase separates into condensates. Mutations that abolish DDX5 prion propagation also impair the protein's ability to phase separate. DDX5 condensates exhibit enhanced enzymatic activity, but they can mature into inactive, solid aggregates. Our findings suggest that protein aggregates with prion-like properties form during normal brain aging, which could have implications for the age-dependency of cognitive decline., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Oxygen deprivation and excess are both toxic. Thus, the body's ability to adapt to varying oxygen tensions is critical for survival. While the hypoxia transcriptional response has been well studied, the post-translational effects of oxygen have been underexplored. In this study, we systematically investigate protein turnover rates in mouse heart, lung, and brain under different inhaled oxygen tensions. We find that the lung proteome is the most responsive to varying oxygen tensions. In particular, several extracellular matrix (ECM) proteins are stabilized in the lung under both hypoxia and hyperoxia. Furthermore, we show that complex 1 of the electron transport chain is destabilized in hyperoxia, in accordance with the exacerbation of associated disease models by hyperoxia and rescue by hypoxia. Moreover, we nominate MYBBP1A as a hyperoxia transcriptional regulator, particularly in the context of rRNA homeostasis. Overall, our study highlights the importance of varying oxygen tensions on protein turnover rates and identifies tissue-specific mediators of oxygen-dependent responses.

Fusion oncoproteins (FOs) arise from chromosomal translocations in ~17% of cancers and are often oncogenic drivers. Although some FOs can promote oncogenesis by undergoing liquid-liquid phase separation (LLPS) to form aberrant biomolecular condensates, the generality of this phenomenon is unknown. We explored this question by testing 166 FOs in HeLa cells and found that 58% formed condensates. The condensate-forming FOs displayed physicochemical features distinct from those of condensate-negative FOs and segregated into distinct feature-based groups that aligned with their sub-cellular localization and biological function. Using Machine Learning, we developed a predictor of FO condensation behavior, and discovered that 67% of ~3000 additional FOs likely form condensates, with 35% of those predicted to function by altering gene expression. 47% of the predicted condensate-negative FOs were associated with cell signaling functions, suggesting a functional dichotomy between condensate-positive and -negative FOs. Our Datasets and reagents are rich resources to interrogate FO condensation in the future., (© 2023. Springer Nature Limited.)

Multicellularity was a watershed development in evolution. However, it also meant that individual cells could escape regulatory mechanisms that restrict proliferation at a severe cost to the organism: cancer. From the standpoint of cellular organization, evolutionary complexity scales to organize different molecules within the intracellular milieu. The recent realization that many biomolecules can "phase-separate" into membraneless organelles, reorganizing cellular biochemistry in space and time, has led to an explosion of research activity in this area. In this review, we explore mechanistic connections between phase separation and cancer-associated processes and emerging examples of how these become deranged in malignancy., Significance: One of the fundamental functions of phase separation is to rapidly and dynamically respond to environmental perturbations. Importantly, these changes often lead to alterations in cancer-relevant pathways and processes. This review covers recent advances in the field, including emerging principles and mechanisms of phase separation in cancer., (©2022 The Authors; Published by the American Association for Cancer Research.)

Background: The brewer's yeast Saccharomyces cerevisiae is exploited in several industrial processes, ranging from food and beverage fermentation to the production of biofuels, pharmaceuticals and complex chemicals. The large genetic and phenotypic diversity within this species offers a formidable natural resource to obtain superior strains, hybrids, and variants. However, most industrially relevant traits in S. cerevisiae strains are controlled by multiple genetic loci. Over the past years, several studies have identified some of these QTLs. However, because these studies only focus on a limited set of traits and often use different techniques and starting strains, a global view of industrially relevant QTLs is still missing., Results: Here, we combined the power of 1125 fully sequenced inbred segregants with high-throughput phenotyping methods to identify as many as 678 QTLs across 18 different traits relevant to industrial fermentation processes, including production of ethanol, glycerol, isobutanol, acetic acid, sulfur dioxide, flavor-active esters, as well as resistance to ethanol, acetic acid, sulfite and high osmolarity. We identified and confirmed several variants that are associated with multiple different traits, indicating that many QTLs are pleiotropic. Moreover, we show that both rare and common variants, as well as variants located in coding and non-coding regions all contribute to the phenotypic variation., Conclusions: Our findings represent an important step in our understanding of the genetic underpinnings of industrially relevant yeast traits and open new routes to study complex genetics and genetic interactions as well as to engineer novel, superior industrial yeasts. Moreover, the major role of rare variants suggests that there is a plethora of different combinations of mutations that can be explored in genome editing., (© 2021. The Author(s).)

In fluctuating environments, switching between different growth strategies, such as those affecting cell size and proliferation, can be advantageous to an organism. Trade-offs arise, however. Mechanisms that aberrantly increase cell size or proliferation-such as mutations or chemicals that interfere with growth regulatory pathways-can also shorten lifespan. Here we report a natural example of how the interplay between growth and lifespan can be epigenetically controlled. We find that a highly conserved RNA-modifying enzyme, the pseudouridine synthase Pus4/TruB, can act as a prion, endowing yeast with greater proliferation rates at the cost of a shortened lifespan. Cells harboring the prion grow larger and exhibit altered protein synthesis. This epigenetic state, [ BIG + ] ( b etter i n g rowth), allows cells to heritably yet reversibly alter their translational program, leading to the differential synthesis of dozens of proteins, including many that regulate proliferation and aging. Our data reveal a new role for prion-based control of an RNA-modifying enzyme in driving heritable epigenetic states that transform cell growth and survival., Competing Interests: DG, CJ, MT, ES, AD, DJ None, EC none, MK Reviewing editor, eLife, (© 2021, Garcia et al.)

Protein aggregation, particularly in its prion-like form, has long been thought to be detrimental. However, recent studies have identified multiple instances where protein aggregation is important for normal physiological functions. Combining mass spectrometry and cell biological approaches, we developed a strategy for the identification of protein aggregates in cell lysates. We used this approach to characterize prion-based traits in pathogenic strains of the yeast Saccharomyces cerevisiae isolated from immunocompromised human patients. The proteins that we found, including the metabolic enzyme Cdc19, the translation elongation factor Yef3 and the fibrillarin homologue Nop1, are known to assemble under certain physiological conditions. Yet, such assemblies have not been reported to be stable or heritable. Our data suggest that some proteins which aggregate in response to stress have the capacity to acquire diverse assembled states, certain ones of which can be propagated across generations in a form of protein-based epigenetics. This article is part of the theme issue 'How does epigenetics influence the course of evolution?'

Prions, proteins that can convert between structurally and functionally distinct states and serve as non-Mendelian mechanisms of inheritance, were initially discovered and only known in eukaryotes, and consequently considered to likely be a relatively late evolutionary acquisition. However, the recent discovery of prions in bacteria and viruses has intimated a potentially more ancient evolutionary origin. Here, we provide evidence that prion-forming domains exist in the domain archaea, the last domain of life left unexplored with regard to prions. We searched for archaeal candidate prion-forming protein sequences computationally, described their taxonomic distribution and phylogeny, and analyzed their associated functional annotations. Using biophysical in vitro assays, cell-based and microscopic approaches, and dye-binding analyses, we tested select candidate prion-forming domains for prionogenic characteristics. Out of the 16 tested, eight formed amyloids, and six acted as protein-based elements of information transfer driving non-Mendelian patterns of inheritance. We also identified short peptides from our archaeal prion candidates that can form amyloid fibrils independently. Lastly, candidates that tested positively in our assays had significantly higher tyrosine and phenylalanine content than candidates that tested negatively, an observation that may help future archaeal prion predictions. Taken together, our discovery of functional prion-forming domains in archaea provides evidence that multiple archaeal proteins are capable of acting as prions-thus expanding our knowledge of this epigenetic phenomenon to the third and final domain of life and bolstering the possibility that they were present at the time of the last universal common ancestor., (Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution 2021.)

Long viewed as paradigm-shifting, but rare, prions have recently been discovered in all domains of life. Protein sequences that can drive this form of self-assembly are strikingly common in eukaryotic proteomes, where they are enriched in proteins involved in information flow and signal transduction. Although prions were thought to be a consequence of random errors in protein folding, recent studies suggest that prion formation can be a controlled process initiated by defined cellular signals. Many are present in normal biological contexts, yet are invisible to most technologies used to interrogate the proteome. Here, we review mechanisms by which protein self-assembly can create a stable record of past stimuli, altering adaptive responses, and how prion behavior is controlled by signaling processes. We touch on the diverse implications that this has for normal biological function and regulation, ranging from drug resistance in fungi to the innate immune response in humans. Finally, we discuss the potential for prion domains in transcription factors and RNA-binding proteins to orchestrate heritable gene expression changes in response to transient signals, such as during development., Competing Interests: Conflict of interest statement Nothing declared., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The complexity of heredity has been appreciated for decades: Many traits are controlled not by a single genetic locus but instead by polymorphisms throughout the genome. The importance of complex traits in biology and medicine has motivated diverse approaches to understanding their detailed genetic bases. Here, we focus on recent systematic studies, many in budding yeast, which have revealed that large numbers of all kinds of molecular variation, from noncoding to synonymous variants, can make significant contributions to phenotype. Variants can affect different traits in opposing directions, and their contributions can be modified by both the environment and the epigenetic state of the cell. The integration of prospective (synthesizing and analyzing variants) and retrospective (examining standing variation) approaches promises to reveal how natural selection shapes quantitative traits. Only by comprehensively understanding nature's genetic tool kit can we predict how phenotypes arise from the complex ensembles of genetic variants in living organisms.

Covalent cysteine modification by reactive oxygen species (ROS) has been implicated in regulating diverse biological processes, yet global understanding of this modification has remained fragmentary. Developing new approaches for detecting cysteine modification, Xiao et al. (2020) recently charted a comprehensive map of cysteine oxidation across tissues and life stages., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Covalent modifications to histones are essential for development, establishing distinct and functional chromatin domains from a common genetic sequence. Whereas repressed chromatin is robustly inherited, no mechanism that facilitates inheritance of an activated domain has been described. Here, we report that the Set3C histone deacetylase scaffold Snt1 can act as a prion that drives the emergence and transgenerational inheritance of an activated chromatin state. This prion, which we term [ESI + ] for expressed sub-telomeric information, is triggered by transient Snt1 phosphorylation upon cell cycle arrest. Once engaged, the prion reshapes the activity of Snt1 and the Set3C complex, recruiting RNA pol II and interfering with Rap1 binding to activate genes in otherwise repressed sub-telomeric domains. This transcriptional state confers broad resistance to environmental stress, including antifungal drugs. Altogether, our results establish a robust means by which a prion can facilitate inheritance of an activated chromatin state to provide adaptive benefit., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Theory and experiments suggest that organisms would benefit from pre-adaptation to future stressors based on reproducible environmental fluctuations experienced by their ancestors, but the mechanisms driving pre-adaptation remain enigmatic. We report that the [SMAUG + ] prion allows yeast to anticipate nutrient repletion after periods of starvation, providing a strong selective advantage. By transforming the landscape of post-transcriptional gene expression, [SMAUG + ] regulates the decision between two broad growth and survival strategies: mitotic proliferation or meiotic differentiation into a stress-resistant state. [SMAUG + ] is common in laboratory yeast strains, where standard propagation practice produces regular cycles of nutrient scarcity followed by repletion. Distinct [SMAUG + ] variants are also widespread in wild yeast isolates from multiple niches, establishing that prion polymorphs can be utilized in natural populations. Our data provide a striking example of how protein-based epigenetic switches, hidden in plain sight, can establish a transgenerational memory that integrates adaptive prediction into developmental decisions., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Spatiotemporal gene regulation is often driven by RNA-binding proteins that harbor long intrinsically disordered regions in addition to folded RNA-binding domains. We report that the disordered region of the evolutionarily ancient developmental regulator Vts1/Smaug drives self-assembly into gel-like condensates. These proteinaceous particles are not composed of amyloid, yet they are infectious, allowing them to act as a protein-based epigenetic element: a prion [SMAUG + ]. In contrast to many amyloid prions, condensation of Vts1 enhances its function in mRNA decay, and its self-assembly properties are conserved over large evolutionary distances. Yeast cells harboring [SMAUG + ] downregulate a coherent network of mRNAs and exhibit improved growth under nutrient limitation. Vts1 condensates formed from purified protein can transform naive cells to acquire [SMAUG + ]. Our data establish that non-amyloid self-assembly of RNA-binding proteins can drive a form of epigenetics beyond the chromosome, instilling adaptive gene expression programs that are heritable over long biological timescales., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The statistical complexity of heredity has long been evident, but its molecular origins remain elusive. To investigate, we charted 90 comprehensive genotype-to-phenotype maps in a large population of wild diploid yeast. In contrast to long-standing assumptions, all types of genetic variation contributed similarly to phenotype. Causal synonymous and regulatory variants exhibited distinct molecular signatures, as did nonlinearities in heterozygote fitness that likely contribute to hybrid vigor. Highly pleiotropic variants altered disordered sequences within signaling hubs, and their effects correlated across environments-even when antagonistic-suggesting that large fitness gains bring concomitant costs. Natural genetic networks defined by the causal loci differed from those determined by precise gene deletions or protein-protein interactions. Finally, we found that traits that would appear omnigenic in less powered studies do in fact have finite genetic determinants. Integrating these molecular principles will be crucial as genome reading and writing become routine in research, industry, and medicine., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Canalization, or phenotypic robustness in the face of environmental and genetic perturbation, is an emergent property of living systems. Although this phenomenon has long been recognized, its molecular underpinnings have remained enigmatic until recently. Here, we review the contributions of the molecular chaperone Hsp90, a protein that facilitates the folding of many key regulators of growth and development, to canalization of phenotype - and de-canalization in times of stress - drawing on studies in eukaryotes as diverse as baker's yeast, mouse ear cress, and blind Mexican cavefish. Hsp90 is a hub of hubs that interacts with many so-called 'client proteins,' which affect virtually every aspect of cell signaling and physiology. As Hsp90 facilitates client folding and stability, it can epistatically suppress or enable the expression of genetic variants in its clients and other proteins that acquire client status through mutation. Hsp90's vast interaction network explains the breadth of its phenotypic reach, including Hsp90-dependent de novo mutations and epigenetic effects on gene regulation. Intrinsic links between environmental stress and Hsp90 function thus endow living systems with phenotypic plasticity in fluctuating environments. As environmental perturbations alter Hsp90 function, they also alter Hsp90's interaction with its client proteins, thereby re-wiring networks that determine the genotype-to-phenotype map. Ensuing de-canalization of phenotype creates phenotypic diversity that is not simply stochastic, but often has an underlying genetic basis. Thus, extreme phenotypes can be selected, and assimilated so that they no longer require environmental stress to manifest. In addition to acting on standing genetic variation, Hsp90 perturbation has also been linked to increased frequency of de novo variation and several epigenetic phenomena, all with the potential to generate heritable phenotypic change. Here, we aim to clarify and discuss the multiple means by which Hsp90 can affect phenotype and possibly evolutionary change, and identify their underlying common feature: at its core, Hsp90 interacts epistatically through its chaperone function with many other genes and their gene products. Its influence on phenotypic diversification is thus not magic but rather a fundamental property of genetics., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Quantitative genetics aims to map genotype to phenotype, often with the goal of understanding how organisms evolved. However, it remains unclear whether the genetic variants identified are exemplary of evolution. Here we analyzed progeny of two wild Saccharomyces cerevisiae isolates to identify 195 loci underlying complex metabolic traits, resolving 107 to single polymorphisms with diverse molecular mechanisms. More than 20% of causal variants exhibited patterns of emergence inconsistent with neutrality. Moreover, contrary to drift-centric expectation, variation in diverse wild yeast isolates broadly exhibited this property: over 30% of shared natural variants exhibited phylogenetic signatures suggesting that they are not neutral. This pattern is likely attributable to both homoplasy and balancing selection on ancestral polymorphism. Variants that emerged repeatedly were more likely to have done so in isolates from the same ecological niche. Our results underscore the power of super-resolution mapping of ecologically relevant traits in understanding adaptation and evolution.

A central tenet of molecular biology is that heritable information is stored in nucleic acids. However, this paradigm has been overturned by a group of proteins called "prions." Prion proteins, many of which are intrinsically disordered, can adopt multiple conformations, at least one of which has the capacity to self-template. This unusual folding landscape drives a form of extreme epigenetic inheritance that can be stable through both mitotic and meiotic cell divisions. Although the first prion discovered-mammalian PrP-is the causative agent of debilitating neuropathies, many additional prions have now been identified that are not obviously detrimental and can even be adaptive. Intrinsically disordered regions, which endow proteins with the bulk property of "phase-separation," can also be drivers of prion formation. Indeed, many protein domains that promote phase separation have been described as prion-like. In this review, we describe how prions lie at the crossroads of phase separation, epigenetic inheritance, and evolutionary adaptation., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

From bacteria to humans, ancient stress responses enable organisms to contend with damage to both the genome and the proteome. These pathways have long been viewed as fundamentally separate responses. Yet recent discoveries from multiple fields have revealed surprising links between the two. Many DNA-damaging agents also target proteins, and mutagenesis induced by DNA damage produces variant proteins that are prone to misfolding, degradation, and aggregation. Likewise, recent studies have observed pervasive engagement of a p53-mediated response, and other factors linked to maintenance of genomic integrity, in response to misfolded protein stress. Perhaps most remarkably, protein aggregation and self-assembly has now been observed in multiple proteins that regulate the DNA damage response. The importance of these connections is highlighted by disease models of both cancer and neurodegeneration, in which compromised DNA repair machinery leads to profound defects in protein quality control, and vice versa., (Copyright © 2018 Elsevier B.V. All rights reserved.)

To survive, organisms must orchestrate competing biochemical and regulatory processes in time and space. Recent work has suggested that the underlying chemical properties of some biomolecules allow them to self-organize and that life may have exploited this property to organize biochemistry in space and time. Such phase separation is ubiquitous, particularly among the many regulatory proteins that harbor prion-like intrinsically disordered domains. And yet, despite evident regulation by post-translational modification and myriad other stimuli, the biological significance of many phase-separated compartments remains uncertain. Many potential functions have been proposed, but far fewer have been demonstrated. A burgeoning subfield at the intersection of cell biology and polymer physics has defined the biophysical underpinnings that govern the genesis and stability of these particles. The picture is complex: many assemblies are composed of multiple proteins that each have the capacity to phase separate. Here, we briefly discuss this foundational work and survey recent efforts combining targeted biochemical perturbations and quantitative modeling to specifically address the diverse roles that phase separation processes may play in biology.

Prion-like proteins have the capacity to adopt multiple stable conformations, at least one of which can recruit proteins from the native conformation into the alternative fold. Although classically associated with disease, prion-like assembly has recently been proposed to organize a range of normal biochemical processes in space and time. Organisms from bacteria to mammals use prion-like mechanisms to (re)organize their proteome in response to intracellular and extracellular stimuli. Prion-like behavior is an economical means to control biochemistry and gene regulation at the systems level, and prions can act as protein-based genes to facilitate quasi-Lamarckian inheritance of induced traits. These mechanisms allow individual cells to express distinct heritable traits using the same complement of polypeptides. Understanding and controlling prion-like behavior is therefore a promising strategy to combat diverse pathologies and organize engineered biological systems.

Understanding the sequence determinants that give rise to diversity among individuals and species is the central challenge of genetics. However, despite ever greater numbers of sequenced genomes, most genome-wide association studies cannot distinguish causal variants from linked passenger mutations spanning many genes. We report that this inherent challenge can be overcome in model organisms. By pushing the advantages of inbred crossing to its practical limit in Saccharomyces cerevisiae, we improved the statistical resolution of linkage analysis to single nucleotides. This "super-resolution" approach allowed us to map 370 causal variants across 26 quantitative traits. Missense, synonymous, and cis-regulatory mutations collectively gave rise to phenotypic diversity, providing mechanistic insight into the basis of evolutionary divergence. Our data also systematically unmasked complex genetic architectures, revealing that multiple closely linked driver mutations frequently act on the same quantitative trait. Single-nucleotide mapping thus complements traditional deletion and overexpression screening paradigms and opens new frontiers in quantitative genetics., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Epigenetics refers to changes in phenotype that are not rooted in DNA sequence. This phenomenon has largely been studied in the context of chromatin modification. Yet many epigenetic traits are instead linked to self-perpetuating changes in the individual or collective activity of proteins. Most such proteins are prions (e.g., [PSI + ], [URE3], [SWI + ], [MOT3 + ], [MPH1 + ], [LSB + ], and [GAR + ]), which have the capacity to adopt at least one conformation that self-templates over long biological timescales. This allows them to serve as protein-based epigenetic elements that are readily broadcast through mitosis and meiosis. In some circumstances, self-templating can fuel disease, but it also permits access to multiple activity states from the same polypeptide and transmission of that information across generations. Ensuing phenotypic changes allow genetically identical cells to express diverse and frequently adaptive phenotypes. Although long thought to be rare, protein-based epigenetic inheritance has now been uncovered in all domains of life., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Protein conformational states-from intrinsically disordered ensembles to amyloids that underlie the self-templating, infectious properties of prion-like proteins-have attracted much attention. Here, we highlight the diversity, including differences in biophysical properties, that drive distinct biological functions and pathologies among self-templating proteins. Advances in chemical genomics, gene editing, and model systems now permit deconstruction of the complex interplay between these protein states and the host factors that react to them. These methods reveal that conformational switches modulate normal and abnormal information transfer and that intimate relationships exist between the intrinsic function of proteins and the deleterious consequences of their misfolding., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The encoding of biological information that is accessible to future generations is generally achieved via changes to the DNA sequence. Long-lived inheritance encoded in protein conformation (rather than sequence) has long been viewed as paradigm-shifting but rare. The best characterized examples of such epigenetic elements are prions, which possess a self-assembling behavior that can drive the heritable manifestation of new phenotypes. Many archetypal prions display a striking N/Q-rich sequence bias and assemble into an amyloid fold. These unusual features have informed most screening efforts to identify new prion proteins. However, at least three known prions (including the founding prion, PrP Sc ) do not harbor these biochemical characteristics. We therefore developed an alternative method to probe the scope of protein-based inheritance based on a property of mass action: the transient overexpression of prion proteins increases the frequency at which they acquire a self-templating conformation. This paper describes a method for analyzing the capacity of the yeast ORFeome to elicit protein-based inheritance. Using this strategy, we previously found that >1% of yeast proteins could fuel the emergence of biological traits that were long-lived, stable, and arose more frequently than genetic mutation. This approach can be employed in high throughput across entire ORFeomes or as a targeted screening paradigm for specific genetic networks or environmental stimuli. Just as forward genetic screens define numerous developmental and signaling pathways, these techniques provide a methodology to investigate the influence of protein-based inheritance in biological processes.

RNA-binding proteins (RBPs) control the fate of nearly every transcript in a cell. However, no existing approach for studying these posttranscriptional gene regulators combines transcriptome-wide throughput and biophysical precision. Here, we describe an assay that accomplishes this. Using commonly available hardware, we built a customizable, open-source platform that leverages the inherent throughput of Illumina technology for direct biophysical measurements. We used the platform to quantitatively measure the binding affinity of the prototypical RBP Vts1 for every transcript in the Saccharomyces cerevisiae genome. The scale and precision of these measurements revealed many previously unknown features of this well-studied RBP. Our transcribed genome array (TGA) assayed both rare and abundant transcripts with equivalent proficiency, revealing hundreds of low-abundance targets missed by previous approaches. These targets regulated diverse biological processes including nutrient sensing and the DNA damage response, and implicated Vts1 in de novo gene "birth." TGA provided single-nucleotide resolution for each binding site and delineated a highly specific sequence and structure motif for Vts1 binding. Changes in transcript levels in vts1 Δ cells established the regulatory function of these binding sites. The impact of Vts1 on transcript abundance was largely independent of where it bound within an mRNA, challenging prevailing assumptions about how this RBP drives RNA degradation. TGA thus enables a quantitative description of the relationship between variant RNA structures, affinity, and in vivo phenotype on a transcriptome-wide scale. We anticipate that TGA will provide similarly comprehensive and quantitative insights into the function of virtually any RBP.

Prions are infectious protein polymers that have been found to cause fatal diseases in mammals. Prions have also been identified in fungi (yeast and filamentous fungi), where they behave as cytoplasmic non-Mendelian genetic elements. Fungal prions correspond in most cases to fibrillary β-sheet-rich protein aggregates termed amyloids. Fungal prion models and, in particular, yeast prions were instrumental in the description of fundamental aspects of prion structure and propagation. These models established the "protein-only" nature of prions, the physical basis of strain variation, and the role of a variety of chaperones in prion propagation and amyloid aggregate handling. Yeast and fungal prions do not necessarily correspond to harmful entities but can have adaptive roles in these organisms.

Robust preference for fermentative glucose metabolism has motivated domestication of the budding yeast Saccharomyces cerevisiae . This program can be circumvented by a protein-based genetic element, the [ GAR + ] prion, permitting simultaneous metabolism of glucose and other carbon sources. Diverse bacteria can elicit yeast cells to acquire [ GAR + ], although the molecular details of this interaction remain unknown. Here we identify the common bacterial metabolite lactic acid as a strong [ GAR + ] inducer. Transient exposure to lactic acid caused yeast cells to heritably circumvent glucose repression. This trait had the defining genetic properties of [ GAR + ], and did not require utilization of lactic acid as a carbon source. Lactic acid also induced [ GAR + ]-like epigenetic states in fungi that diverged from S. cerevisiae ~200 million years ago, and in which glucose repression evolved independently. To our knowledge, this is the first study to uncover a bacterial metabolite with the capacity to potently induce a prion., Competing Interests: JC: Reviewing editor, eLife. The other authors declare that no competing interests exist.

Prions are a paradigm-shifting mechanism of inheritance in which phenotypes are encoded by self-templating protein conformations rather than nucleic acids. Here, we examine the breadth of protein-based inheritance across the yeast proteome by assessing the ability of nearly every open reading frame (ORF; ∼5,300 ORFs) to induce heritable traits. Transient overexpression of nearly 50 proteins created traits that remained heritable long after their expression returned to normal. These traits were beneficial, had prion-like patterns of inheritance, were common in wild yeasts, and could be transmitted to naive cells with protein alone. Most inducing proteins were not known prions and did not form amyloid. Instead, they are highly enriched in nucleic acid binding proteins with large intrinsically disordered domains that have been widely conserved across evolution. Thus, our data establish a common type of protein-based inheritance through which intrinsically disordered proteins can drive the emergence of new traits and adaptive opportunities., (Copyright © 2016 Elsevier Inc. All rights reserved.)

In experimental science, organisms are usually studied in isolation, but in the wild, they compete and cooperate in complex communities. We report a system for cross-kingdom communication by which bacteria heritably transform yeast metabolism. An ancient biological circuit blocks yeast from using other carbon sources in the presence of glucose. [GAR(+)], a protein-based epigenetic element, allows yeast to circumvent this "glucose repression" and use multiple carbon sources in the presence of glucose. Some bacteria secrete a chemical factor that induces [GAR(+)]. [GAR(+)] is advantageous to bacteria because yeast cells make less ethanol and is advantageous to yeast because their growth and long-term viability is improved in complex carbon sources. This cross-kingdom communication is broadly conserved, providing a compelling argument for its adaptive value. By heritably transforming growth and survival strategies in response to the selective pressures of life in a biological community, [GAR(+)] presents a unique example of Lamarckian inheritance., (Copyright © 2014 Elsevier Inc. All rights reserved.)

[GAR(+)] is a protein-based element of inheritance that allows yeast (Saccharomyces cerevisiae) to circumvent a hallmark of their biology: extreme metabolic specialization for glucose fermentation. When glucose is present, yeast will not use other carbon sources. [GAR(+)] allows cells to circumvent this "glucose repression." [GAR(+)] is induced in yeast by a factor secreted by bacteria inhabiting their environment. We report that de novo rates of [GAR(+)] appearance correlate with the yeast's ecological niche. Evolutionarily distant fungi possess similar epigenetic elements that are also induced by bacteria. As expected for a mechanism whose adaptive value originates from the selective pressures of life in biological communities, the ability of bacteria to induce [GAR(+)] and the ability of yeast to respond to bacterial signals have been extinguished repeatedly during the extended monoculture of domestication. Thus, [GAR(+)] is a broadly conserved adaptive strategy that links environmental and social cues to heritable changes in metabolism., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Prions are proteins that convert between structurally and functionally distinct states, at least one of which is self-perpetuating. The prion fold templates the conversion of native protein, altering its structure and function, and thus serves as a protein-based element of inheritance. Molecular chaperones ensure that these prion aggregates are divided and faithfully passed from mother cells to their daughters. Prions were originally identified as the cause of several rare neurodegenerative diseases in mammals, but the last decade has brought great progress in understanding their broad importance in biology and evolution. Most prion proteins regulate information flow in signaling networks, or otherwise affect gene expression. Consequently, switching into and out of prion states creates diverse new traits – heritable changes based on protein structure rather than nucleic acid. Despite intense study of the molecular mechanisms of this paradigm-shifting, epigenetic mode of inheritance, many key questions remain. Recent studies in yeast that support the view that prions are common, often beneficial elements of inheritance that link environmental stress to the appearance of new traits.

In the process of morphological evolution, the extent to which cryptic, preexisting variation provides a substrate for natural selection has been controversial. We provide evidence that heat shock protein 90 (HSP90) phenotypically masks standing eye-size variation in surface populations of the cavefish Astyanax mexicanus. This variation is exposed by HSP90 inhibition and can be selected for, ultimately yielding a reduced-eye phenotype even in the presence of full HSP90 activity. Raising surface fish under conditions found in caves taxes the HSP90 system, unmasking the same phenotypic variation as does direct inhibition of HSP90. These results suggest that cryptic variation played a role in the evolution of eye loss in cavefish and provide the first evidence for HSP90 as a capacitor for morphological evolution in a natural setting.

The self-templating conformations of yeast prion proteins act as epigenetic elements of inheritance. Yeast prions might provide a mechanism for generating heritable phenotypic diversity that promotes survival in fluctuating environments and the evolution of new traits. However, this hypothesis is highly controversial. Prions that create new traits have not been found in wild strains, leading to the perception that they are rare 'diseases' of laboratory cultivation. Here we biochemically test approximately 700 wild strains of Saccharomyces for [PSI(+)] or [MOT3(+)], and find these prions in many. They conferred diverse phenotypes that were frequently beneficial under selective conditions. Simple meiotic re-assortment of the variation harboured within a strain readily fixed one such trait, making it robust and prion-independent. Finally, we genetically screened for unknown prion elements. Fully one-third of wild strains harboured them. These, too, created diverse, often beneficial phenotypes. Thus, prions broadly govern heritable traits in nature, in a manner that could profoundly expand adaptive opportunities.

How can species remain unaltered for long periods yet also undergo rapid diversification? By linking genetic variation to phenotypic variation via environmental stress, the Hsp90 protein-folding reservoir might promote both stasis and change. However, the nature and adaptive value of Hsp90-contingent traits remain uncertain. In ecologically and genetically diverse yeasts, we find such traits to be both common and frequently adaptive. Most are based on preexisting variation, with causative polymorphisms occurring in coding and regulatory sequences alike. A common temperature stress alters phenotypes similarly. Both selective inhibition of Hsp90 and temperature stress increase correlations between genotype and phenotype. This system broadly determines the adaptive value of standing genetic variation and, in so doing, has influenced the evolution of current genomes.

Heat shock protein 90 (HSP90) is a highly conserved molecular chaperone that facilitates the maturation of a wide range of proteins (known as clients). Clients are enriched in signal transducers, including kinases and transcription factors. Therefore, HSP90 regulates diverse cellular functions and exerts marked effects on normal biology, disease and evolutionary processes. Recent structural and functional analyses have provided new insights on the transcriptional and biochemical regulation of HSP90 and the structural dynamics it uses to act on a diverse client repertoire. Comprehensive understanding of how HSP90 functions promises not only to provide new avenues for therapeutic intervention, but to shed light on fundamental biological questions.

Changing a single nucleotide in a genome can have profound consequences under some conditions, but the same change can have no consequences under others. Indeed, organisms can be surprisingly robust to environmental and genetic perturbations. Yet, the mechanisms underlying such robustness are controversial. Moreover, how they might affect evolutionary change remains enigmatic. Here, we review the recently appreciated central role of protein homeostasis in buffering and potentiating genetic variation and discuss how these processes mediate the critical influence of the environment on the relationship between genotype and phenotype. Deciphering how robustness emerges from biological organization and the mechanisms by which it is overcome in changing environments will lead to a more complete understanding of both fundamental evolutionary processes and diverse human diseases.

The only Y-family DNA polymerase conserved among all domains of life, DinB and its mammalian ortholog pol kappa, catalyzes proficient bypass of damaged DNA in translesion synthesis (TLS). Y-family DNA polymerases, including DinB, have been implicated in diverse biological phenomena ranging from adaptive mutagenesis in bacteria to several human cancers. Complete TLS requires dNTP insertion opposite a replication blocking lesion and subsequent extension with several dNTP additions. Here we report remarkably proficient TLS extension by DinB from Escherichia coli. We also describe a TLS DNA polymerase variant generated by mutation of an evolutionarily conserved tyrosine (Y79). This mutant DinB protein is capable of catalyzing dNTP insertion opposite a replication-blocking lesion, but cannot complete TLS, stalling three nucleotides after an N(2)-dG adduct. Strikingly, expression of this variant transforms a bacteriostatic DNA damaging agent into a bactericidal drug, resulting in profound toxicity even in a dinB(+) background. We find that this phenomenon is not exclusively due to a futile cycle of abortive TLS followed by exonucleolytic reversal. Rather, gene products with roles in cell death and metal homeostasis modulate the toxicity of DinB(Y79L) expression. Together, these results indicate that DinB is specialized to perform remarkably proficient insertion and extension on damaged DNA, and also expose unexpected connections between TLS and cell fate.

DinB is the only translesion Y family DNA polymerase conserved among bacteria, archaea, and eukaryotes. DinB and its orthologs possess a specialized lesion bypass function but also display potentially deleterious -1 frameshift mutagenic phenotypes when overproduced. We show that the DNA damage-inducible proteins UmuD(2) and RecA act in concert to modulate this mutagenic activity. Structural modeling suggests that the relatively open active site of DinB is enclosed by interaction with these proteins, thereby preventing the template bulging responsible for -1 frameshift mutagenesis. Intriguingly, residues that define the UmuD(2)-interacting surface on DinB statistically covary throughout evolution, suggesting a driving force for the maintenance of a regulatory protein-protein interaction at this site. Together, these observations indicate that proteins like RecA and UmuD(2) may be responsible for managing the mutagenic potential of DinB orthologs throughout evolution.

Reactive oxygen and nitrogen radicals produced during metabolic processes, such as respiration and inflammation, combine with DNA to form many lesions primarily at guanine sites. Understanding the roles of the polymerases responsible for the processing of these products to mutations could illuminate molecular mechanisms that correlate oxidative stress with cancer. Using M13 viral genomes engineered to contain single DNA lesions and Escherichia coli strains with specific polymerase (pol) knockouts, we show that pol V is required for efficient bypass of structurally diverse, highly mutagenic guanine oxidation products in vivo. We also find that pol IV participates in the bypass of two spiroiminodihydantoin lesions. Furthermore, we report that one lesion, 5-guanidino-4-nitroimidazole, is a substrate for multiple SOS polymerases, whereby pol II is necessary for error-free replication and pol V for error-prone replication past this lesion. The results spotlight a major role for pol V and minor roles for pol II and pol IV in the mechanism of guanine oxidation mutagenesis.