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Background Information: Commitment to splicing occurs co-transcriptionally, but a major unanswered question is the extent to which various modifications of chromatin, the template for transcription in vivo, contribute to the regulation of splicing., Results: Here, we perform genome-wide analyses showing that inhibition of specific marks - H2B ubiquitylation, H3K4 methylation and H3K36 methylation - perturbs splicing in budding yeast, with each modification exerting gene-specific effects. Furthermore, semi-quantitative mass spectrometry on purified nuclear mRNPs and chromatin immunoprecipitation analysis on intron-containing genes indicated that H2B ubiquitylation, but not Set1-, Set2- or Dot1-dependent H3 methylation, stimulates recruitment of the early splicing factors, namely U1 and U2 snRNPs, onto nascent RNAs., Conclusions: These results suggest that histone modifications impact splicing of distinct subsets of genes using distinct pathways., (© 2014 Société Française des Microscopies and Société de Biologie Cellulaire de France. Published by John Wiley & Sons Ltd.)

Previously a ring finger protein 20 (RNF20) is found to be essential for meiotic recombination and mediates H2B ubiquitination during spermatogenesis. However, its role in meiotic division is still unknown. Here, it is shown that RNF20 is localized at both centromeres and spindle poles, and it is required for oocyte acentrosomal spindle organization and female fertility. RNF20‐depleted oocytes exhibit severely abnormal spindle and chromosome misalignment caused by defective bipolar organization. Notably, it is found that the function of RNF20 in spindle assembly is not dependent on its E3 ligase activity. Instead, RNF20 regulates spindle assembly by recruiting tropomyosin3 (TPM3) to both centromeres and spindle poles with its coiled‐coil motif. The RNF20‐TPM3 interaction is essential for acentrosomal meiotic spindle assembly. Together, the studies uncover a novel function for RNF20 in mediating TPM3 recruitment to both centromeres and spindle poles during oocyte spindle assembly. [ABSTRACT FROM AUTHOR]

The discrete steps of transcriptional rewiring have been proposed to occur neutrally to ensure steady gene expression under stabilizing selection. A conflict‐free switch of a regulon between regulators may require an immediate compensatory evolution to minimize deleterious effects. Here, we perform an evolutionary repair experiment on the Lachancea kluyveri yeast sef1Δ mutant using a suppressor development strategy. Complete loss of SEF1 forces cells to initiate a compensatory process for the pleiotropic defects arising from misexpression of TCA cycle genes. Using different selective conditions, we identify two adaptive loss‐of‐function mutations of IRA1 and AZF1. Subsequent analyses show that Azf1 is a weak transcriptional activator regulated by the Ras1‐PKA pathway. Azf1 loss‐of‐function triggers extensive gene expression changes responsible for compensatory, beneficial, and trade‐off phenotypes. The trade‐offs can be alleviated by higher cell density. Our results not only indicate that secondary transcriptional perturbation provides rapid and adaptive mechanisms potentially stabilizing the initial stage of transcriptional rewiring but also suggest how genetic polymorphisms of pleiotropic mutations could be maintained in the population. Synopsis: Evolutionary repair in sef1Δ mutant cells of the yeast Lachancea kluyveri highlights the rapid adaptive strategies to handle growth defects and to compensate for gene misexpression. Adaptive clones evolve rapidly in populations of sef1Δ cells under different selective conditions.Loss‐of‐function or hypomorphic mutations pervasively hit two genes, IRA1 and AZF1, which are responsible for the adaptive phenotypes.The pleiotropy of loss‐of‐function azf1 mutations has beneficial fitness and compensatory effects under favorable conditions but results in growth trade‐offs when encountering unfavorable conditions.The growth trade‐offs of azf1 genotypes can be alleviated by increasing the cell density in unfavorable conditions. [ABSTRACT FROM AUTHOR]

Cell growth and quiescence in eukaryotic cells is controlled by an evolutionarily conserved network of signaling pathways. Signal transduction networks operate to modulate a wide range of cellular processes and physiological properties when cells exit proliferative growth and initiate a quiescent state. How signaling networks function to respond to diverse signals that result in cell cycle exit and establishment of a quiescent state is poorly understood. Here, we studied the function of signaling pathways in quiescent cells using global genetic interaction mapping in the model eukaryotic cell, Saccharomyces cerevisiae (budding yeast). We performed pooled analysis of genotypes using molecular barcode sequencing (Bar‐seq) to test the role of ~4,000 gene deletion mutants and ~12,000 pairwise interactions between all non‐essential genes and the protein kinase genes TOR1,RIM15, and PHO85 in three different nutrient‐restricted conditions in both proliferative and quiescent cells. We detect up to 10‐fold more genetic interactions in quiescent cells than proliferative cells. We find that both individual gene effects and genetic interaction profiles vary depending on the specific pro‐quiescence signal. The master regulator of quiescence, RIM15, shows distinct genetic interaction profiles in response to different starvation signals. However, vacuole‐related functions show consistent genetic interactions with RIM15 in response to different starvation signals, suggesting that RIM15 integrates diverse signals to maintain protein homeostasis in quiescent cells. Our study expands genome‐wide genetic interaction profiling to additional conditions, and phenotypes, and highlights the conditional dependence of epistasis. Synopsis: A pooled analysis of genotypes using Bar‐seq shows that the genetic and functional requirements of proliferative and quiescent cells differ between conditions. Quantitative genetic interaction mapping reveals condition‐dependent genetic interaction profiles for the core regulatory kinases. Genetic interactions in thousands of mutants are studied using pooled assays and time series analyses using Bar‐seq, enabling efficient study of additional phenotypes such as survival of nutrient starvation.The genetic interactions of the signaling kinase genes TOR1, RIM15, PHO85 vary between different environmental conditions and cellular states.RIM15 interacts with similar functional classes of genes in different starvation conditions consistent with its role as a master regulator of quiescence.Unique and cohesive positive genetic interactions between RIM15 and Endoplasmic‐reticulum‐associated protein degradation (ERAD) genes point to a new functional relationship when responding to nitrogen starvation. [ABSTRACT FROM AUTHOR]

Pab1, the major poly (A) binding protein of the yeast Saccharomyces cerevisiae, is involved in many intracellular functions associated with mRNA metabolism, such as mRNA nuclear export, deadenylation, translation initiation and termination. Pab1 consists of four RNA recognition motifs (RRM), a proline‐rich domain (P) and a carboxy‐terminal (C) domain. Due to its modular structure, Pab1 can simultaneously interact with poly (A) tails and different proteins that regulate mRNA turnover and translation. Furthermore, Pab1 also influences cell physiology under stressful conditions by affecting the formation of quinary assemblies and stress granules, as well as by stabilizing specific mRNAs to allow translation re‐initiation after stress. The main goal of this review is to correlate the structural complexity of this protein with the multiplicity of its functions. [ABSTRACT FROM AUTHOR]

Living systems control cell growth dynamically by processing information from their environment. Although responses to a single environmental change have been intensively studied, little is known about how cells react to fluctuating conditions. Here, we address this question at the genomic scale by measuring the relative proliferation rate (fitness) of 3,568 yeast gene deletion mutants in out-of-equilibrium conditions: periodic oscillations between two environmental conditions. In periodic salt stress, fitness and its genetic variance largely depended on the oscillating period. Surprisingly, dozens of mutants displayed pronounced hyperproliferation under short stress periods, revealing unexpected controllers of growth under fast dynamics. We validated the implication of the high-affinity cAMP phosphodiesterase and of a regulator of protein translocation to mitochondria in this group. Periodic oscillations of extracellular methionine, a factor unrelated to salinity, also altered fitness but to a lesser extent and for different genes. The results illustrate how natural selection acts on mutations in a dynamic environment, highlighting unsuspected genetic vulnerabilities to periodic stress in molecular processes that are conserved across all eukaryotes. [ABSTRACT FROM AUTHOR]

Transcription, RNA processing, and chromatin-related factors all interact with RNA polymerase II (Pol II) to ensure proper timing and coordination of transcription and co-transcriptional processes. Many transcription elongation regulators must function simultaneously to coordinate these processes, yet few strategies exist to explore the complement of factors regulating specific stages of transcription. To this end, we developed a strategy to purify Pol II elongation complexes from subgenic regions of a single gene, namely the 5′ and 3′ regions, using sequences in the nascent RNA. Applying this strategy to Saccharomyces cerevisiae, we determined the specific set of factors that interact with Pol II at precise stages during transcription. We identify many known region-specific factors as well as determine unappreciated associations of regulatory factors during early and late stages of transcription. These data reveal a role for the transcription termination factor, Rai1, in regulating the early stages of transcription genome-wide and support the role of Bye1 as a negative regulator of early elongation. We also demonstrate a role for the ubiquitin ligase, Bre1, in regulating Pol II dynamics during the latter stages of transcription. These data and our approach to analyze subgenic transcription elongation complexes will shed new light on the myriad factors that regulate the different stages of transcription and coordinate co-transcriptional processes. [ABSTRACT FROM AUTHOR]

Monoubiquitination of histone H2B (to H2Bub1) is required for downstream events including histone H3 methylation, transcription, and mRNA export. The mechanisms and players regulating these events have not yet been completely delineated. Here, we show that the conserved Ran‐binding protein Mog1 is required to sustain normal levels of H2Bub1 and H3K4me3 in Saccharomyces cerevisiae. Mog1 is needed for gene body recruitment of Rad6, Bre1, and Rtf1 that are involved in H2B ubiquitination and genetically interacts with these factors. We provide evidence that the absence of MOG1 impacts on cellular processes such as transcription, DNA replication, and mRNA export, which are linked to H2Bub1. Importantly, the mRNA export defect in mog1Δ strains is exacerbated by the absence of factors that decrease H2Bub1 levels. Consistent with a role in sustaining H2Bub and H3K4me3 levels, Mog1 co‐precipitates with components that participate in these modifications such as Bre1, Rtf1, and the COMPASS‐associated factors Shg1 and Sdc1. These results reveal a novel role for Mog1 in H2B ubiquitination, transcription, and mRNA biogenesis. Synopsis: The conserved Mog1 protein is important for H2Bub1, H3K4me3, transcription, and mRNA export. This novel role is distinct from its known ability to bind Ran‐GTP during protein transport. Mog1 is required to sustain normal levels of H2Bub1 and H3K4me3 and co‐precipitates with components that participate in these modifications in Saccharomyces cerevisiae.The absence of MOG1 impacts on cellular processes linked to H2Bub1, such as transcription and mRNA export.Mog1 binding to Ran is not required for its role in epigenetic modifications. The conserved Mog1 protein is important for H2Bub1, H3K4me3, transcription, and mRNA export. This novel role is distinct from its known ability to bind Ran‐GTP during protein transport. [ABSTRACT FROM AUTHOR]