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In transcription-coupled nucleotide excision repair (TC-NER), stalled RNA polymerase II (RNA Pol II) binds CSB and CRL4 CSA , which cooperate with UVSSA and ELOF1 to recruit TFIIH. To explore the mechanism of TC-NER, we recapitulated this reaction in vitro. When a plasmid containing a site-specific lesion is transcribed in frog egg extract, error-free repair is observed that depends on CSB, CRL4 CSA , UVSSA, and ELOF1. Repair also requires STK19, a factor previously implicated in transcription recovery after UV exposure. A 1.9-Å cryo-electron microscopy structure shows that STK19 binds the TC-NER complex through CSA and the RPB1 subunit of RNA Pol II. Furthermore, AlphaFold predicts that STK19 interacts with the XPD subunit of TFIIH, and disrupting this interface impairs cell-free repair. Molecular modeling suggests that STK19 positions TFIIH ahead of RNA Pol II for lesion verification. Our analysis of cell-free TC-NER suggests that STK19 couples RNA Pol II stalling to downstream repair events., Competing Interests: Declaration of interests J.C.W. is a co-founder of MOMA Therapeutics, in which he has a financial interest., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

In eukaryotic cells, transcription by RNA polymerase II occurs in the context of chromatin, requiring the transcription machinery to navigate through nucleosomes as it traverses gene bodies. Recent advances in structural biology have provided unprecedented insights into the mechanisms underlying transcription elongation. This review presents a structural perspective on transcription through chromatin, focusing on the latest findings from high-resolution structures of transcribing RNA polymerase II-nucleosome complexes. I discuss how RNA polymerase II, in concert with elongation factors such as SPT4/5, SPT6, ELOF1, and the PAF1 complex, engages with and transcribes through nucleosomes. The review examines the stepwise unwrapping of nucleosomal DNA as polymerase advances, the roles of elongation factors in facilitating this process, and the mechanisms of nucleosome retention and transfer during transcription. This structural perspective provides a foundation for understanding the intricate interplay between the transcription machinery and chromatin, offering insights into how cells balance the need for genetic accessibility with the maintenance of genome stability and epigenetic regulation., 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 Elsevier Ltd. All rights reserved.)

To maintain the nucleosome organization of transcribed genes, ATP-dependent chromatin remodelers collaborate with histone chaperones. Here, we show that at the 5' ends of yeast genes, RNA polymerase II (RNAPII) generates hexasomes that occur directly adjacent to nucleosomes. The resulting hexasome-nucleosome complexes are then resolved by Chd1. We present two cryoelectron microscopy (cryo-EM) structures of Chd1 bound to a hexasome-nucleosome complex before and after restoration of the missing inner H2A/H2B dimer by FACT. Chd1 uniquely interacts with the complex, positioning its ATPase domain to shift the hexasome away from the nucleosome. In the absence of the inner H2A/H2B dimer, its DNA-binding domain (DBD) packs against the ATPase domain, suggesting an inhibited state. Restoration of the dimer by FACT triggers a rearrangement that displaces the DBD and stimulates Chd1 remodeling. Our results demonstrate how chromatin remodelers interact with a complex nucleosome assembly and suggest how Chd1 and FACT jointly support transcription by RNAPII., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Nucleosomes are the fundamental unit of eukaryotic chromatin. Diverse factors interact with nucleosomes to modulate chromatin architecture and facilitate DNA repair, replication, transcription, and other cellular processes. An important platform for chromatin binding is the H2A-H2B acidic patch. Here, we used AlphaFold-Multimer to screen over 7000 human proteins for nucleosomal acidic patch binding and identify 41 potential acidic patch binders. We determined the cryo-EM structure of one hit, SHPRH, with the nucleosome at 2.8 Å. The structure confirms the predicted acidic patch interaction, reveals that the SHPRH ATPase engages a different nucleosomal DNA location than other SF2-type ATPases, and clarifies the roles of SHPRH's domains in nucleosome recognition. Our results illustrate the use of in silico screening as a high throughput method to identify specific interaction types and expands the set of potential acidic patch binding factors., All the Screening Data Is Freely Available at: https://predictomes.org/view/acidicpatch.

Acetylation of histones is a key post-translational modification that guides gene expression regulation. In yeast, the class I histone deacetylase containing Rpd3S complex plays a critical role in the suppression of spurious transcription by removing histone acetylation from actively transcribed genes. The S. cerevisiae Rpd3S complex has five subunits (Rpd3, Sin3, Rco1, Eaf3, and Ume1) but its subunit stoichiometry and how the complex engages nucleosomes to achieve substrate specificity remains elusive. Here we report the cryo-EM structure of the complete Rpd3S complex bound to a nucleosome. Sin3 and two copies of subunits Rco1 and Eaf3 encircle the deacetylase subunit Rpd3 and coordinate the positioning of Ume1. The Rpd3S complex binds both trimethylated H3 tails at position lysine 36 and makes multiple additional contacts with the nucleosomal DNA and the H2A-H2B acidic patch. Direct regulation via the Sin3 subunit coordinates binding of the acetylated histone substrate to achieve substrate specificity., (© 2023. The Author(s).)

Transcription of most protein-coding genes requires the passage of RNA polymerase II through chromatin. Chromatin with its fundamental unit, the nucleosome, represents a barrier to transcription. How RNA polymerase II and associated factors traverse through nucleosomes and how chromatin architecture is maintained have remained largely enigmatic. Only recently, cryo-EM structures have visualized the transcription process through chromatin. These structures have elucidated how transcription initiation and transcription elongation influence and are influenced by a chromatinized DNA substrate. This review provides a summary of our current structural understanding of transcription through chromatin, highlighting common mechanisms during nucleosomal traversal and novel regulatory mechanisms that have emerged in the last five years., 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 © 2023 Elsevier Ltd. All rights reserved.)

Co-transcriptional capping of the nascent pre-mRNA 5' end prevents degradation of RNA polymerase (Pol) II transcripts and suppresses the innate immune response. Here, we provide mechanistic insights into the three major steps of human co-transcriptional pre-mRNA capping based on six different cryoelectron microscopy (cryo-EM) structures. The human mRNA capping enzyme, RNGTT, first docks to the Pol II stalk to position its triphosphatase domain near the RNA exit site. The capping enzyme then moves onto the Pol II surface, and its guanylyltransferase receives the pre-mRNA 5'-diphosphate end. Addition of a GMP moiety can occur when the RNA is ∼22 nt long, sufficient to reach the active site of the guanylyltransferase. For subsequent cap(1) methylation, the methyltransferase CMTR1 binds the Pol II stalk and can receive RNA after it is grown to ∼29 nt in length. The observed rearrangements of capping factors on the Pol II surface may be triggered by the completion of catalytic reaction steps and are accommodated by domain movements in the elongation factor DRB sensitivity-inducing factor (DSIF)., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The reversible acetylation of histone lysine residues is controlled by the action of acetyltransferases and deacetylases (HDACs), which regulate chromatin structure and gene expression. The sirtuins are a family of NAD-dependent HDAC enzymes, and one member, sirtuin 6 (Sirt6), influences DNA repair, transcription, and aging. Here, we demonstrate that Sirt6 is efficient at deacetylating several histone H3 acetylation sites, including its canonical site Lys9, in the context of nucleosomes but not free acetylated histone H3 protein substrates. By installing a chemical warhead at the Lys9 position of histone H3, we trap a catalytically poised Sirt6 in complex with a nucleosome and employ this in cryo-EM structural analysis. The structure of Sirt6 bound to a nucleosome reveals extensive interactions between distinct segments of Sirt6 and the H2A/H2B acidic patch and nucleosomal DNA, which accounts for the rapid deacetylation of nucleosomal H3 sites and the disfavoring of histone H2B acetylation sites. These findings provide a new framework for understanding how HDACs target and regulate chromatin.

During gene transcription, RNA polymerase II (RNA Pol II) passes nucleosomes with the help of various elongation factors. Here, we show that RNA Pol II achieves efficient nucleosome passage when the human elongation factors DSIF, PAF1 complex (PAF), RTF1, SPT6, and TFIIS are present. The cryo-EM structure of an intermediate of the nucleosome passage shows a partially unraveled hexasome that lacks the proximal H2A-H2B dimer and interacts with the RNA Pol II jaw, DSIF, and the CTR9trestle helix. RNA Pol II adopts a backtracked state with the RNA 3' end dislodged from the active site and bound in the RNA Pol II pore. Additional structures and biochemical data show that human TFIIS enters the RNA Pol II pore and stimulates the cleavage of the backtracked RNA and nucleosome passage., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)

In eukaryotes, RNA polymerase (Pol) II transcribes chromatin and must move past nucleosomes, often resulting in nucleosome displacement. How Pol II unwraps the DNA from nucleosomes to allow transcription and how DNA rewraps to retain nucleosomes has been unclear. Here, we report the 3.0-angstrom cryo-electron microscopy structure of a mammalian Pol II-DSIF-SPT6-PAF1c-TFIIS-nucleosome complex stalled 54 base pairs within the nucleosome. The structure provides a mechanistic basis for nucleosome retention during transcription elongation where upstream DNA emerging from the Pol II cleft has rewrapped the proximal side of the nucleosome. The structure uncovers a direct role for Pol II and transcription elongation factors in nucleosome retention and explains how nucleosomes are retained to prevent the disruption of chromatin structure across actively transcribed genes.

The first step of eukaryotic gene expression is the assembly of RNA polymerase II and general transcription factors on promoter DNA. This highly regulated process involves ∼80 different proteins that together form the preinitiation complex (PIC). Decades of work have gone into understanding PIC assembly using biochemical and structural approaches. These efforts have yielded significant but partial descriptions of PIC assembly. Over the past few years, cryo-electron microscopy has provided the first high-resolution structures of the near-complete mammalian PIC assembly. These structures have revealed that PIC assembly is a highly dynamic process. This review will summarize recent structural findings and discuss their implications for understanding cell type-specific gene expression., Competing Interests: Conflict of interest statement Nothing declared., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Transcription by RNA polymerase II (RNA Pol II) relies on the elongation factors PAF1 complex (PAF), RTF1, and SPT6. Here, we use rapid factor depletion and multi-omics analysis to investigate how these elongation factors influence RNA Pol II elongation activity in human cells. Whereas depletion of PAF subunits PAF1 and CTR9 has little effect on cellular RNA synthesis, depletion of RTF1 or SPT6 strongly compromises RNA Pol II activity, albeit in fundamentally different ways. RTF1 depletion decreases RNA Pol II velocity, whereas SPT6 depletion impairs RNA Pol II progression through nucleosomes. These results show that distinct elongation factors stimulate either RNA Pol II velocity or RNA Pol II progression through chromatin in vivo. Further analysis provides evidence for two distinct barriers to early elongation: the promoter-proximal pause site and the +1 nucleosome. It emerges that the first barrier enables loading of elongation factors that are required to overcome the second and subsequent barriers to transcription., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Arrays of regularly spaced nucleosomes dominate chromatin and are often phased by alignment to reference sites like active promoters. How the distances between nucleosomes (spacing), and between phasing sites and nucleosomes are determined remains unclear, and specifically, how ATP-dependent chromatin remodelers impact these features. Here, we used genome-wide reconstitution to probe how Saccharomyces cerevisiae ATP-dependent remodelers generate phased arrays of regularly spaced nucleosomes. We find that remodelers bear a functional element named the 'ruler' that determines spacing and phasing in a remodeler-specific way. We use structure-based mutagenesis to identify and tune the ruler element residing in the Nhp10 and Arp8 modules of the INO80 remodeler complex. Generally, we propose that a remodeler ruler regulates nucleosome sliding direction bias in response to (epi)genetic information. This finally conceptualizes how remodeler-mediated nucleosome dynamics determine stable steady-state nucleosome positioning relative to other nucleosomes, DNA bound factors, DNA ends and DNA sequence elements.

Efficient transcription of RNA polymerase II (Pol II) through nucleosomes requires the help of various factors. Here we show biochemically that Pol II transcription through a nucleosome is facilitated by the chromatin remodeler Chd1 and the histone chaperone FACT when the elongation factors Spt4/5 and TFIIS are present. We report cryo-EM structures of transcribing Saccharomyces cerevisiae Pol II-Spt4/5-nucleosome complexes with bound Chd1 or FACT. In the first structure, Pol II transcription exposes the proximal histone H2A-H2B dimer that is bound by Spt5. Pol II has also released the inhibitory DNA-binding region of Chd1 that is poised to pump DNA toward Pol II. In the second structure, Pol II has generated a partially unraveled nucleosome that binds FACT, which excludes Chd1 and Spt5. These results suggest that Pol II progression through a nucleosome activates Chd1, enables FACT binding and eventually triggers transfer of FACT together with histones to upstream DNA.

Remdesivir is the only FDA-approved drug for the treatment of COVID-19 patients. The active form of remdesivir acts as a nucleoside analog and inhibits the RNA-dependent RNA polymerase (RdRp) of coronaviruses including SARS-CoV-2. Remdesivir is incorporated by the RdRp into the growing RNA product and allows for addition of three more nucleotides before RNA synthesis stalls. Here we use synthetic RNA chemistry, biochemistry and cryo-electron microscopy to establish the molecular mechanism of remdesivir-induced RdRp stalling. We show that addition of the fourth nucleotide following remdesivir incorporation into the RNA product is impaired by a barrier to further RNA translocation. This translocation barrier causes retention of the RNA 3'-nucleotide in the substrate-binding site of the RdRp and interferes with entry of the next nucleoside triphosphate, thereby stalling RdRp. In the structure of the remdesivir-stalled state, the 3'-nucleotide of the RNA product is matched and located with the template base in the active center, and this may impair proofreading by the viral 3'-exonuclease. These mechanistic insights should facilitate the quest for improved antivirals that target coronavirus replication.

The new coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) uses an RNA-dependent RNA polymerase (RdRp) for the replication of its genome and the transcription of its genes 1-3 . Here we present a cryo-electron microscopy structure of the SARS-CoV-2 RdRp in an active form that mimics the replicating enzyme. The structure comprises the viral proteins non-structural protein 12 (nsp12), nsp8 and nsp7, and more than two turns of RNA template-product duplex. The active-site cleft of nsp12 binds to the first turn of RNA and mediates RdRp activity with conserved residues. Two copies of nsp8 bind to opposite sides of the cleft and position the second turn of RNA. Long helical extensions in nsp8 protrude along exiting RNA, forming positively charged 'sliding poles'. These sliding poles can account for the known processivity of RdRp that is required for replicating the long genome of coronaviruses 3 . Our results enable a detailed analysis of the inhibitory mechanisms that underlie the antiviral activity of substances such as remdesivir, a drug for the treatment of coronavirus disease 2019 (COVID-19) 4 .

Transcription by RNA polymerase II (Pol II) is carried out by an elongation complex. We previously reported an activated porcine Pol II elongation complex, EC*, encompassing the human elongation factors DSIF, PAF1 complex (PAF) and SPT6. Here we report the cryo-EM structure of the complete EC* that contains RTF1, a dissociable PAF subunit critical for chromatin transcription. The RTF1 Plus3 domain associates with Pol II subunit RPB12 and the phosphorylated C-terminal region of DSIF subunit SPT5. RTF1 also forms four α-helices that extend from the Plus3 domain along the Pol II protrusion and RPB10 to the polymerase funnel. The C-terminal 'fastener' helix retains PAF and is followed by a 'latch' that reaches the end of the bridge helix, a flexible element of the Pol II active site. RTF1 strongly stimulates Pol II elongation, and this requires the latch, possibly suggesting that RTF1 activates transcription allosterically by influencing Pol II translocation.

Chromatin remodeling plays important roles in gene regulation during development, differentiation and in disease. The chromatin remodeling enzyme CHD4 is a component of the NuRD and ChAHP complexes that are involved in gene repression. Here, we report the cryo-electron microscopy (cryo-EM) structure of Homo sapiens CHD4 engaged with a nucleosome core particle in the presence of the non-hydrolysable ATP analogue AMP-PNP at an overall resolution of 3.1 Å. The ATPase motor of CHD4 binds and distorts nucleosomal DNA at superhelical location (SHL) +2, supporting the 'twist defect' model of chromatin remodeling. CHD4 does not induce unwrapping of terminal DNA, in contrast to its homologue Chd1, which functions in gene activation. Our structure also maps CHD4 mutations that are associated with human cancer or the intellectual disability disorder Sifrim-Hitz-Weiss syndrome., Competing Interests: LF, MO, PC No competing interests declared, (© 2020, Farnung et al.)

Recognition of histone-modified nucleosomes by specific reader domains underlies the regulation of chromatin-associated processes. Whereas structural studies revealed how reader domains bind modified histone peptides, it is unclear how reader domains interact with modified nucleosomes. Here, we report the cryo-electron microscopy structure of the PWWP reader domain of human transcriptional coactivator LEDGF in complex with an H3K36-methylated nucleosome at 3.2-Å resolution. The structure reveals multivalent binding of the reader domain to the methylated histone tail and to both gyres of nucleosomal DNA, explaining the known cooperative interactions. The observed cross-gyre binding may contribute to nucleosome integrity during transcription. The structure also explains how human PWWP domain-containing proteins are recruited to H3K36-methylated regions of the genome for transcription, histone acetylation and methylation, and for DNA methylation and repair.

Transcription of eukaryotic protein-coding genes requires passage of RNA polymerase II (Pol II) through nucleosomes, but it is unclear how this is achieved. Here we report the cryo-EM structure of transcribing Saccharomyces cerevisiae Pol II engaged with a downstream nucleosome core particle at an overall resolution of 4.4 Å. Pol II and the nucleosome are observed in a defined relative orientation that is not predicted. Pol II contacts both sides of the nucleosome dyad using its clamp head and lobe domains. Structural comparisons reveal that the elongation factors TFIIS, DSIF, NELF, SPT6, and PAF1 complex can be accommodated on the Pol II surface in the presence of the oriented nucleosome. Our results provide a starting point for analysing the mechanisms of chromatin transcription.

Nucleosomes cover most of the genome and are thought to be displaced by transcription factors in regions that direct gene expression. However, the modes of interaction between transcription factors and nucleosomal DNA remain largely unknown. Here we systematically explore interactions between the nucleosome and 220 transcription factors representing diverse structural families. Consistent with earlier observations, we find that the majority of the studied transcription factors have less access to nucleosomal DNA than to free DNA. The motifs recovered from transcription factors bound to nucleosomal and free DNA are generally similar. However, steric hindrance and scaffolding by the nucleosome result in specific positioning and orientation of the motifs. Many transcription factors preferentially bind close to the end of nucleosomal DNA, or to periodic positions on the solvent-exposed side of the DNA. In addition, several transcription factors usually bind to nucleosomal DNA in a particular orientation. Some transcription factors specifically interact with DNA located at the dyad position at which only one DNA gyre is wound, whereas other transcription factors prefer sites spanning two DNA gyres and bind specifically to each of them. Our work reveals notable differences in the binding of transcription factors to free and nucleosomal DNA, and uncovers a diverse interaction landscape between transcription factors and the nucleosome.

Gene regulation involves activation of RNA polymerase II (Pol II) that is paused and bound by the protein complexes DRB sensitivity-inducing factor (DSIF) and negative elongation factor (NELF). Here we show that formation of an activated Pol II elongation complex in vitro requires the kinase function of the positive transcription elongation factor b (P-TEFb) and the elongation factors PAF1 complex (PAF) and SPT6. The cryo-EM structure of an activated elongation complex of Sus scrofa Pol II and Homo sapiens DSIF, PAF and SPT6 was determined at 3.1 Å resolution and compared to the structure of the paused elongation complex formed by Pol II, DSIF and NELF. PAF displaces NELF from the Pol II funnel for pause release. P-TEFb phosphorylates the Pol II linker to the C-terminal domain. SPT6 binds to the phosphorylated C-terminal-domain linker and opens the RNA clamp formed by DSIF. These results provide the molecular basis for Pol II pause release and elongation activation.

Metazoan gene regulation often involves the pausing of RNA polymerase II (Pol II) in the promoter-proximal region. Paused Pol II is stabilized by the protein complexes DRB sensitivity-inducing factor (DSIF) and negative elongation factor (NELF). Here we report the cryo-electron microscopy structure of a paused transcription elongation complex containing Sus scrofa Pol II and Homo sapiens DSIF and NELF at 3.2 Å resolution. The structure reveals a tilted DNA-RNA hybrid that impairs binding of the nucleoside triphosphate substrate. NELF binds the polymerase funnel, bridges two mobile polymerase modules, and contacts the trigger loop, thereby restraining Pol II mobility that is required for pause release. NELF prevents binding of the anti-pausing transcription elongation factor IIS (TFIIS). Additionally, NELF possesses two flexible 'tentacles' that can contact DSIF and exiting RNA. These results define the paused state of Pol II and provide the molecular basis for understanding the function of NELF during promoter-proximal gene regulation.

RNA polymerase II (Pol II) is the central enzyme that transcribes eukaryotic protein-coding genes to produce mRNA. The mushroom toxin α-amanitin binds Pol II and inhibits transcription at the step of RNA chain elongation. Pol II from yeast binds α-amanitin with micromolar affinity, whereas metazoan Pol II enzymes exhibit nanomolar affinities. Here, we present the high-resolution cryo-EM structure of α-amanitin bound to and inhibited by its natural target, the mammalian Pol II elongation complex. The structure revealed that the toxin is located in a pocket previously identified in yeast Pol II but forms additional contacts with metazoan-specific residues, which explains why its affinity to mammalian Pol II is ∼3000 times higher than for yeast Pol II. Our work provides the structural basis for the inhibition of mammalian Pol II by the natural toxin α-amanitin and highlights that cryo-EM is well suited to studying interactions of a small molecule with its macromolecular target., (© 2018 Liu et al.)

Several anticancer agents that form DNA adducts in the minor groove interfere with DNA replication and transcription to induce apoptosis. Therapeutic resistance can occur, however, when cells are proficient in the removal of drug-induced damage. Acylfulvenes are a class of experimental anticancer agents with a unique repair profile suggesting their capacity to stall RNA polymerase (Pol) II and trigger transcription-coupled nucleotide excision repair. Here we show how different forms of DNA alkylation impair transcription by RNA Pol II in cells and with the isolated enzyme and unravel a mode of RNA Pol II stalling that is due to alkylation of DNA in the minor groove. We incorporated a model for acylfulvene adducts, the stable 3-deaza-3-methoxynaphtylethyl-adenosine analog (3d-Napht-A), and smaller 3-deaza-adenosine analogs, into DNA oligonucleotides to assess RNA Pol II transcription elongation in vitro. RNA Pol II was strongly blocked by a 3d-Napht-A analog but bypassed smaller analogs. Crystal structure analysis revealed that a DNA base containing 3d-Napht-A can occupy the +1 templating position and impair closing of the trigger loop in the Pol II active center and polymerase translocation into the next template position. These results show how RNA Pol II copes with minor-groove DNA alkylation and establishes a mechanism for drug resistance., Competing Interests: The authors declare no conflict of interest., (Copyright © 2017 the Author(s). Published by PNAS.)

Chromatin-remodelling factors change nucleosome positioning and facilitate DNA transcription, replication, and repair. The conserved remodelling factor chromodomain-helicase-DNA binding protein 1(Chd1) can shift nucleosomes and induce regular nucleosome spacing. Chd1 is required for the passage of RNA polymerase IIthrough nucleosomes and for cellular pluripotency. Chd1 contains the DNA-binding domains SANT and SLIDE, a bilobal motor domain that hydrolyses ATP, and a regulatory double chromodomain. Here we report the cryo-electron microscopy structure of Chd1 from the yeast Saccharomyces cerevisiae bound to a nucleosome at a resolution of 4.8 Å. Chd1 detaches two turns of DNA from the histone octamer and binds between the two DNA gyres in a state poised for catalysis. The SANT and SLIDE domains contact detached DNA around superhelical location (SHL) -7 of the first DNA gyre. The ATPase motor binds the second DNA gyre at SHL +2 and is anchored to the N-terminal tail of histone H4, as seen in a recent nucleosome-Snf2 ATPase structure. Comparisons with published results reveal that the double chromodomain swings towards nucleosomal DNA at SHL +1, resulting in ATPase closure. The ATPase can then promote translocation of DNA towards the nucleosome dyad, thereby loosening the first DNA gyre and remodelling the nucleosome. Translocation may involve ratcheting of the two lobes of the ATPase, which is trapped in a pre- or post-translocation state in the absence or presence, respectively, of transition state-mimicking compounds.

In eukaryotes, gene expression depends on chromatin organization. However, how chromatin affects the transcription dynamics of individual RNA polymerases has remained elusive. Here, we use dual trap optical tweezers to study single yeast RNA polymerase II (Pol II) molecules transcribing along a DNA template with two nucleosomes. The slowdown and the changes in pausing behavior within the nucleosomal region allow us to determine a drift coefficient, χ , which characterizes the ability of the enzyme to recover from a nucleosomal backtrack. Notably, χ can be used to predict the probability to pass the first nucleosome. Importantly, the presence of a second nucleosome changes χ in a manner that depends on the spacing between the two nucleosomes, as well as on their rotational arrangement on the helical DNA molecule. Our results indicate that the ability of Pol II to pass the first nucleosome is increased when the next nucleosome is turned away from the first one to face the opposite side of the DNA template. These findings help to rationalize how chromatin arrangement affects Pol II transcription dynamics., Competing Interests: The authors declare no conflict of interest.

Phosphorylation of the RNA polymerase II C-terminal domain (CTD) by cyclin-dependent kinases is important for productive transcription. Here we determine the crystal structure of Cdk12/CycK and analyse its requirements for substrate recognition. Active Cdk12/CycK is arranged in an open conformation similar to that of Cdk9/CycT but different from those of cell cycle kinases. Cdk12 contains a C-terminal extension that folds onto the N- and C-terminal lobes thereby contacting the ATP ribose. The interaction is mediated by an HE motif followed by a polybasic cluster that is conserved in transcriptional CDKs. Cdk12/CycK showed the highest activity on a CTD substrate prephosphorylated at position Ser7, whereas the common Lys7 substitution was not recognized. Flavopiridol is most potent towards Cdk12 but was still 10-fold more potent towards Cdk9. T-loop phosphorylation of Cdk12 required coexpression with a Cdk-activating kinase. These results suggest the regulation of Pol II elongation by a relay of transcriptionally active CTD kinases.