转录延伸因子ELOF1基因的功能

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The protein IWS1 (Interacts with SPT6 1) is implicated in transcription-associated processes, but a direct role in RNA polymerase (Pol) II function is unknown. Here, we use multi-omics kinetic analysis after rapid depletion of IWS1 in human cells to show that loss of IWS1 results in a global decrease of RNA synthesis and a global reduction in Pol II elongation velocity. We then resolve the cryo-EM structure of the activated Pol II elongation complex with bound IWS1 and elongation factor ELOF1 and show that IWS1 acts as a scaffold and positions downstream DNA within the cleft of Pol II. In vitro assays show that the disordered C-terminal region of IWS1 that contacts the cleft of Pol II is responsible for stimulation of Pol II activity and is aided by ELOF1. Finally, we find that the defect in transcription upon IWS1 depletion leads to a decrease of histone H3 tri-methylation at residue lysine-36 (H3K36me3), but that this secondary effect is an indirect function of IWS1. In summary, our structure-function analysis establishes IWS1 as a Pol II-associated elongation factor that acts globally to stimulate Pol II elongation velocity and ensure proper co-transcriptional histone methylation.

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Transcription elongation by RNA polymerase II is a tightly regulated process that requires coordinated interactions between transcription elongation factors. IWS1 (Interacts with SPT6) has been implicated as a core elongation factor, but its molecular role remains unclear. We show that the intrinsically disordered C-terminal region of IWS1 contains short linear motifs (SLiMs) that multivalently engage the elongation machinery. Using cryo-electron microscopy, we map SLiMs in IWS1 that interact with Pol II subunits RPB1, RPB2, and RPB5, as well as elongation factors DSIF, SPT6, and ELOF1. Functional assays demonstrate that distinct IWS1 SLiMs specify IWS1 recruitment and IWS1-dependent transcription stimulation. IWS1 recruitment to the transcription elongation complex depends on association via the RPB1 jaw and binding of downstream DNA. Transcription elongation stimulation requires interactions with the RPB2 lobe and ELOF1. We identify other transcription elongation factors including ELOA and RECQL5 that bind the RPB1 jaw and demonstrate that IWS1 protects the activated transcription elongation complex from RECQL5 inhibition. We also reveal the binding of the histone reader and IWS1 interactor LEDGF to a transcribed downstream nucleosome. Our findings establish IWS1 as a modular scaffold that helps organize the transcription elongation complex, illustrating how disordered regions regulate transcription elongation.

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Transcription-coupled nucleotide excision repair (TC-NER) is a highly conserved DNA repair pathway that removes bulky lesions in the transcribed genome. Cockayne syndrome B protein (CSB), or its yeast ortholog Rad26, has been known for decades to play important roles in the lesion-recognition steps of TC-NER. Another conserved protein ELOF1, or its yeast ortholog Elf1, was recently identified as a core transcription-coupled repair factor. How Rad26 distinguishes between RNA polymerase II (Pol II) stalled at a DNA lesion or other obstacles and what role Elf1 plays in this process remains unknown. Here, we present cryo-EM structures of Pol II-Rad26 complexes stalled at different obstacles that show that Rad26 uses a common mechanism to recognize a stalled Pol II, with additional interactions when Pol II is arrested at a lesion. A cryo-EM structure of lesion-arrested Pol II-Rad26 bound to Elf1 revealed that Elf1 induces further interactions between Rad26 and a lesion-arrested Pol II. Biochemical and genetic data support the importance of the interplay between Elf1 and Rad26 in TC-NER initiation. Together, our results provide important mechanistic insights into how two conserved transcription-coupled repair factors, Rad26/CSB and Elf1/ELOF1, work together at the initial lesion recognition steps of transcription-coupled repair.

XPA is a central scaffold protein that coordinates the assembly of repair complexes in the global genome (GG-NER) and transcription-coupled nucleotide excision repair (TC-NER) subpathways. Inactivating mutations in XPA cause xeroderma pigmentosum (XP), which is characterized by extreme UV sensitivity and a highly elevated skin cancer risk. Here, we describe two Dutch siblings in their late forties carrying a homozygous H244R substitution in the C-terminus of XPA. They present with mild cutaneous manifestations of XP without skin cancer but suffer from marked neurological features, including cerebellar ataxia. We show that the mutant XPA protein has a severely weakened interaction with the transcription factor IIH (TFIIH) complex leading to an impaired association of the mutant XPA and the downstream endonuclease ERCC1-XPF with NER complexes. Despite these defects, the patient-derived fibroblasts and reconstituted knockout cells carrying the XPA-H244R substitution show intermediate UV sensitivity and considerable levels of residual GG-NER (~50%), in line with the intrinsic properties and activities of the purified protein. By contrast, XPA-H244R cells are exquisitely sensitive to transcription-blocking DNA damage, show no detectable recovery of transcription after UV irradiation, and display a severe deficiency in TC-NER-associated unscheduled DNA synthesis. Our characterization of a new case of XPA deficiency that interferes with TFIIH binding and primarily affects the transcription-coupled subpathway of nucleotide excision repair, provides an explanation of the dominant neurological features in these patients, and reveals a specific role for the C-terminus of XPA in TC-NER.

SUMMARY The response to DNA damage is critical for cellular homeostasis, tumor suppression, immunity and gametogenesis. In order to provide an unbiased and global view of the DNA damage response in human cells, we undertook 28 CRISPR/Cas9 screens against 25 genotoxic agents in the retinal pigment epithelium-1 (RPE1) cell line. These screens identified 840 genes whose loss causes either sensitivity or resistance to DNA damaging agents. Mining this dataset, we uncovered that ERCC6L2 , which is mutated in a bone-marrow failure syndrome, codes for a canonical non-homologous end-joining pathway factor; that the RNA polymerase II component ELOF1 modulates the response to transcription-blocking agents and that the cytotoxicity of the G-quadruplex ligand pyridostatin involves trapping topoisomerase II on DNA. This map of the DNA damage response provides a rich resource to study this fundamental cellular system and has implications for the development and use of genotoxic agents in cancer therapy.

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DNA damage severely impedes gene transcription by RNA polymerase II (Pol II), causing cellular dysfunction. Transcription-Coupled Nucleotide Excision Repair (TC-NER) specifically removes such transcription-blocking damage. TC-NER initiation relies on the CSB, CSA and UVSSA proteins; loss of any results in complete TC-NER deficiency. Strikingly, UVSSA deficiency results in UV-Sensitive Syndrome (UVSS), with mild cutaneous symptoms, while loss of CSA or CSB activity results in the severe Cockayne Syndrome (CS), characterized by neurodegeneration and premature aging. Thus far the underlying mechanism for these contrasting phenotypes remains unclear. Live-cell imaging approaches reveal that in TC-NER proficient cells, lesion-stalled Pol II is swiftly resolved, while in CSA and CSB knockout (KO) cells, elongating Pol II remains damage-bound, likely obstructing other DNA transacting processes and shielding the damage from alternative repair pathways. In contrast, in UVSSA KO cells, Pol II is cleared from the damage via VCP-mediated proteasomal degradation which is fully dependent on the CRL4CSA ubiquitin ligase activity. This Pol II degradation might provide access for alternative repair mechanisms, such as GG-NER, to remove the damage. Collectively, our data indicate that the inability to clear lesion-stalled Pol II from the chromatin, rather than TC-NER deficiency, causes the severe phenotypes observed in CS.

Protein-DNA damage interactions are critical for understanding the mechanism of DNA repair and damage response. However, due to the relatively random distributions of UV-induced damage and other DNA bulky adducts, it is challenging to measure the interactions between proteins and these lesions across the genome. To address this issue, we developed a new method named Protein-Associated DNA Damage Sequencing (PADD-seq) that uses Damage-seq to detect damage distribution in chromatin immunoprecipitation-enriched DNA fragments. It is possible to delineate genome-wide protein-DNA damage interactions at base resolution with this strategy. Using PADD-seq, we observed that RNA polymerase II (Pol II) was blocked by UV-induced damage on template strands, and the interaction declined within 2 h in transcription-coupled repair-proficient cells. On the other hand, Pol II was clearly restrained at damage sites in the absence of the transcription-repair coupling factor CSB during the same time course. Furthermore, we used PADD-seq to examine local changes in H3 acetylation at lysine 9 (H3K9ac) around cisplatin-induced damage, demonstrating the method's broad utility. In conclusion, this new method provides a powerful tool for monitoring the dynamics of protein-DNA damage interaction at the genomic level, and it encourages comprehensive research into DNA repair and damage response.

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.

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Abstract Faithful transcription of eukaryotic genes by RNA polymerase II (Pol II) is essential for proper cell function. Nevertheless, the integrity of the DNA template of Pol II is continuously challenged by different sources of DNA damage, such as UV-light, that impede transcription. When unresolved, these transcription-blocking lesions (TBLs) can cause cellular dysfunction, senescence and apoptosis, eventually resulting in DNA damage-induced aging. Cells counteract these deleterious effects by Transcription-Coupled Nucleotide Excision Repair (TC-NER), which specifically removes TBLs, thereby safeguarding transcription. TC-NER initiation relies on the concerted actions of the CSB, CSA and UVSSA proteins, and loss of either of these factors results in a complete TC-NER deficiency. Although their TC-NER defect is similar, UVSSA loss results in UV-Sensitive Syndrome (UV S S), with only mild phenotypes like freckling and photosensitivity, while loss of CSA or CSB activity results in the severe Cockayne Syndrome (CS), characterized by premature aging, progressive neurodegeneration and mental retardation. Thus far the underlying mechanism for these striking differences in phenotypes remains unclear. Using live-cell imaging approaches, here we show that in TC-NER proficient cells lesion-stalled Pol II is swiftly resolved by repair of the TBL. However, in CSA and CSB knockout (KO) cells, elongating Pol II remains chromatin-bound. This lesion-stalled Pol II will obstruct other DNA transacting processes and will also shield the damage from repair by alternative pathways. In contrast, in UVSSA KO cells, Pol II is removed from the TBL by VCP-mediated proteasomal degradation, thereby, allowing alternative repair mechanisms to remove the TBL.

e15149 Background: Cells possess a complex DNA damage response (DDR) system to prevent detrimental mutations from accumulating. The genes encoding various DDR components are frequently mutated in cancer cells and provide potential sites for therapeutic intervention. DNA damaging agents, with one exception, are repaired by the global genome nucleotide excision repair (GG-NER) pathway. Our novel class of drugs, Illudins, are the exception as Illudin-induced DNA damage is not recognized by GG-NER and can only be repaired by the transcription-coupled nucleotide excision repair (TC-NER) pathway. Studies utilizing isogeneic cell lines completely deficient in specific TC-NER proteins (e.g. homozygous ERCC6 knockout) indicate these cells are extremely sensitive to Illudins (up to 30-fold). In contrast, cells deficient in GG-NER activity are not sensitive to our drugs. Moreover, non-replicating or normal cells are minimally affected by Illudins, as evidenced by the lack of systemic toxicity in humans treated with one of our drugs. In TC-NER deficient cancer cells, however, our drug ITX-0121 blocks the TC-NER polymerase complex, which disengages from DNA, and initiates the irreversible process of apoptosis or cellular suicide. Many cancers exhibit deficiencies in DDR mechanisms and cannot properly repair DNA damage. Methods: Analysis of the GENIE Database indicates that the overall incidence of TC-NER deficient cancers in solid tumors is ~10%, and includes all major histological classifications (breast, ovarian, endometrial, prostate, renal, bladder, bone, colorectal, liver, lung, skin, pancreatic, thyroid, etc.) or ~175,000 new patients annually. These cancers, however, possess monoallelic mutations, as opposed to biallelic, and thus have some residual TC-NER functionality. To determine the relative sensitivity of cancers with monoallelic alterations in TC-NER genes, we generated colorectal HCT-116 cells with a monoallelic deletion in a single TC-NER gene. For example, we are generating daughter cell lines with small monoallelic deletions in ERCC2, ERCC3, ERCC4, ERCC6, and ELOF1 genes. Results: We are comparing sensitivity of these daughter lines to our lead drug ITX-0121, as well as to other DNA damaging agents such as cisplatin. Preliminary results indicate a monoallelic alteration in a TC-NER gene can confer > 6-fold sensitivity to ITX-0121, which is clinically relevant based on PK results. Based on these PK results, we believe the maximum tolerated dose (MTD) of ITX-0121 in patients to be > 1.2 mg/kg; yet only 0.4 mg/kg will be sufficient for clinical efficacy against cancers that are phenotypically TC-NER deficient. Conclusions: Thus, despite the administration of a cytotoxic agent, TC-NER deficient cancer patients can be treated at a non-toxic dose; if toxicity occurs, it should be limited to transient thrombocytopenia, as indicated by prior studies.

Congenital nucleotide excision repair (NER) deficiency gives rise to several cancer-prone and/or progeroid disorders. It is not understood how defects in the same DNA repair pathway cause different disease features and severity. Here, we show that the absence of functional ERCC1-XPF or XPG endonucleases leads to stable and prolonged binding of the transcription/DNA repair factor TFIIH to DNA damage, which correlates with disease severity and induces senescence features in human cells. In vivo, in C. elegans, this prolonged TFIIH binding to non-excised DNA damage causes developmental arrest and neuronal dysfunction, in a manner dependent on transcription-coupled NER. NER factors XPA and TTDA both promote stable TFIIH DNA binding and their depletion therefore suppresses these severe phenotypical consequences. These results identify stalled NER intermediates as pathogenic to cell functionality and organismal development, which can in part explain why mutations in XPF or XPG cause different disease features than mutations in XPA or TTDA.

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In the early stage of transcription, eukaryotic RNA polymerase II (Pol II) exchanges initiation factors with elongation factors to form an elongation complex for processive transcription. Here we report the structure of the Pol II elongation complex bound with the basal elongation factors Spt4/5, Elf1, and TFIIS. Spt4/5 (the Spt4/Spt5 complex) and Elf1 modify a wide area of the Pol II surface. Elf1 bridges the Pol II central cleft, completing a "DNA entry tunnel" for downstream DNA. Spt4 and the Spt5 NGN and KOW1 domains encircle the upstream DNA, constituting a "DNA exit tunnel." The Spt5 KOW4 and KOW5 domains augment the "RNA exit tunnel," directing the exiting nascent RNA. Thus, the elongation complex establishes a completely different transcription and regulation platform from that of the initiation complexes.

RNA polymerase II (RNAPII) transcribes chromosomal DNA that contains multiple nucleosomes. The nucleosome forms transcriptional barriers, and nucleosomal transcription requires several additional factors in vivo. We demonstrate that the transcription elongation factors Elf1 and Spt4/5 cooperatively lower the barriers and increase the RNAPII processivity in the nucleosome. The cryo-electron microscopy structures of the nucleosome-transcribing RNAPII elongation complexes (ECs) reveal that Elf1 and Spt4/5 reshape the EC downstream edge and intervene between RNAPII and the nucleosome. They facilitate RNAPII progression through superhelical location SHL(-1) by adjusting the nucleosome in favor of the forward progression. They suppress pausing at SHL(-5) by preventing the stable RNAPII-nucleosome interaction. Thus, the EC overcomes the nucleosomal barriers while providing a platform for various chromatin functions.

During gene transcription, RNA polymerase II (RNAPII) traverses nucleosomes in chromatin, but the mechanism has remained elusive. Using cryo-electron microscopy, we obtained structures of the RNAPII elongation complex (EC) passing through a nucleosome in the presence of the transcription elongation factors Spt6, Spn1, Elf1, Spt4/5, and Paf1C and the histone chaperone FACT (facilitates chromatin transcription). The structures show snapshots of EC progression on DNA mediating downstream nucleosome disassembly, followed by its reassembly upstream of the EC, which is facilitated by FACT. FACT dynamically adapts to successively occurring subnucleosome intermediates, forming an interface with the EC. Spt6, Spt4/5, and Paf1C form a "cradle" at the EC DNA-exit site and support the upstream nucleosome reassembly. These structures explain the mechanism by which the EC traverses nucleosomes while maintaining the chromatin structure and epigenetic information.

RNA polymerase II elongation complexes (ECs) were assembled from nuclear extract on immobilized DNA templates and analyzed by quantitative mass spectrometry. Time-course experiments showed that initiation factor TFIIF can remain bound to early ECs, while levels of core elongation factors Spt4-Spt5, Paf1C, Spt6-Spn1, and Elf1 remain steady. Importantly, the dynamic phosphorylation patterns of the Rpb1 C-terminal domain (CTD) and the factors that recognize them change as a function of postinitiation time rather than distance elongated. Chemical inhibition of Kin28/Cdk7 in vitro blocks both Ser5 and Ser2 phosphorylation, affects initiation site choice, and inhibits elongation efficiency. EC components dependent on CTD phosphorylation include capping enzyme, cap-binding complex, Set2, and the polymerase-associated factor (PAF1) complex. By recapitulating many known features of in vivo elongation, this system reveals new details that clarify how EC-associated factors change at each step of transcription.

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Nucleotide excision repair removes UV-induced DNA damage through two distinct sub-pathways, global repair and transcription-coupled repair (TCR). Numerous studies have shown that in human and other mammalian cell lines that the XPC protein is required for repair of DNA damage from nontranscribed DNA via global repair and the CSB protein is required for repair of lesions from transcribed DNA via TCR. Therefore, it is generally assumed that abrogating both sub-pathways with an XPC-/-/CSB-/- double mutant would eliminate all nucleotide excision repair. Here we describe the construction of three different XPC-/-/CSB-/- human cell lines that, contrary to expectations, perform TCR. The XPC and CSB genes were mutated in cell lines derived from Xeroderma Pigmentosum patients as well as from normal human fibroblasts and repair was analyzed at the whole genome level using the very sensitive XR-seq method. As predicted, XPC-/- cells exhibited only TCR and CSB-/- cells exhibited only global repair. However, the XPC-/-/CSB-/- double mutant cell lines, although having greatly reduced repair, exhibited TCR. Mutating the CSA gene to generate a triple mutant XPC-/-/CSB-/-/CSA-/- cell line eliminated all residual TCR activity. Together, these findings provide new insights into the mechanistic features of mammalian nucleotide excision repair.

Abstract DNA lesions block the progression of RNA polymerase II (RNAPII) during transcription, impeding gene expression and threatening genome integrity. When RNAPII stalls on transcription-blocking lesions, the transcription-coupled DNA repair pathway is activated to remove the DNA damage. Following DNA repair, efficient transcription restart depends on the PAF1 elongation complex (PAF1C). PAF1C contributes to deposition of transcription-associated histone marks, including H2B-K120 Ub , H3K4me 3 and H3K79me 2 . These marks are enriched at actively transcribed genes and have been associated with regulation of post-repair transcription restart. Here, we show that the H2B-K120 E3 ubiquitin ligase RNF20/RNF40, the H3K4-methyltransferase SET1/COMPASS complex, and the H3K79-methyltransferase DOT1L are dispensable for transcription restart. Moreover, levels of H2B-K120 Ub and H3K4me 3 do not correlate with transcription restoration following DNA damage. Additionally, we observe that, unlike PAF1, the dissociable PAF1C subunit RTF1, while stimulating H2B-K120 Ub and H3K4me 3 , does not play a role in transcription restart. Together, these data suggest that transcription restoration after DNA damage is stimulated by the PAF1C elongation complex, independently of transcription-associated histone mark deposition.

Transcription-coupled nucleotide excision repair (TC-NER or TCR) is initiated when the ATPase Cockayne syndrome protein B (CSB) recognizes a DNA lesion stalled RNA polymerase II (RNAPII) and forms a stable complex. Here, we report that poly(ADP-ribose) polymerase-1 (PARP1), that plays a key role in the lesion recognition step of global genomic NER, also facilitates the earliest step of TCR. PARP1, which is associated with RNAPII during normal transcription, interacts with and stabilizes CSB on the lesion-stalled RNAPII. CSB stimulates PARP1's activity to form PAR, and in turn CSB is PARylated mainly at its N-terminal PAR-binding motif (PBM) to promote its stabilization with RNAPII, whereas its minor PARylation at the C-terminal domain suppresses its ATPase function, thus limiting the window of time for ATP-dependent lesion recognition by CSB. The loss of PARP1, treatment with inhibitors of PARP or poly(ADP-ribose) glycohydrolase (PARG) to prevent PAR synthesis or its catabolism to generate free PAR or engineering N-terminal PARylation-resistant CSB decrease the efficiency of cells for TCR. PARP1 mutant Caenorhabditis elegans larvae exhibit a pronounced TCR-deficient phenotype. Our findings uncover an evolutionarily conserved role of PARP1 and PAR metabolism in the initiation of TCR.

Dissecting the mechanism of and identifying factors involved in the DNA damage-induced transcription stress response.