Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.6 (RNA polymerase)
 34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transcription coupled repair (TC-NER) is a subpathway of nucleotide excision repair triggered by stalling of RNA polymerase at DNA lesions. It has been suspected that transcriptional misincorporations of certain nucleotides opposite lesions that result in irreversible transcription stalling might be important for TC-NER. However, the spectra of nucleotide misincorporations opposite UV photoproducts and how they are implicated in transcriptional stalling and TC-NER in the cell remain unknown. Rad26, a low abundant yeast protein, and its human homolog CSB have been proposed to facilitate TC-NER in part by positioning and stabilizing stalling of RNA polymerase II (RNAPII) at DNA lesions. Here, we found that substantial AMPs but no other nucleotides are transcriptionally misincoporated and extended opposite UV photoproducts and adjacent bases in Saccharomyces cerevisiae. Rad26 does not significantly affect either the misincorporation or extension of AMPs. At normally low or moderately increased levels, Rad26 promotes error-free transcriptional bypass and TC-NER of UV photoproducts. However, Rad26 completely loses these functions when it is overexpressed to ~1/3 the level of RNAPII molecules. Also, Rad26 does not directly displace RNAPII but constitutively evicts Spt5, a key transcription elongation factor and TC-NER repressor, from the chromatin. Our results indicate that transcriptional nucleotide misincorporation is not implicated in TC-NER, and moderate eviction of Spt5 and promotion of error-free transcriptional bypass of DNA lesions by Rad26 facilitates TC-NER.
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PMID:Evidence that Moderate Eviction of Spt5 and Promotion of Error-Free Transcriptional Bypass by Rad26 Facilitates Transcription Coupled Nucleotide Excision Repair. 3079 Jun 31

Cockayne Syndrome (CS) is a severe neurodegenerative and premature aging autosomal-recessive disease, caused by inherited defects in the CSA and CSB genes, leading to defects in transcription-coupled nucleotide excision repair (TC-NER) and consequently hypersensitivity to ultraviolet (UV) irradiation. TC-NER is initiated by lesion-stalled RNA polymerase II, which stabilizes the interaction with the SNF2/SWI2 ATPase CSB to facilitate recruitment of the CSA E3 Cullin ubiquitin ligase complex. However, the precise biochemical connections between CSA and CSB are unknown. The small ubiquitin-like modifier SUMO is important in the DNA damage response. We found that CSB, among an extensive set of other target proteins, is the most dynamically SUMOylated substrate in response to UV irradiation. Inhibiting SUMOylation reduced the accumulation of CSB at local sites of UV irradiation and reduced recovery of RNA synthesis. Interestingly, CSA is required for the efficient clearance of SUMOylated CSB. However, subsequent proteomic analysis of CSA-dependent ubiquitinated substrates revealed that CSA does not ubiquitinate CSB in a UV-dependent manner. Surprisingly, we found that CSA is required for the ubiquitination of the largest subunit of RNA polymerase II, RPB1. Combined, our results indicate that the CSA, CSB, RNA polymerase II triad is coordinated by ubiquitin and SUMO in response to UV irradiation. Furthermore, our work provides a resource of SUMO targets regulated in response to UV or ionizing radiation.
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PMID:Transcription-coupled nucleotide excision repair is coordinated by ubiquitin and SUMO in response to ultraviolet irradiation. 3172 99

Transcription-coupled repair (TCR) removes DNA lesions from the transcribed strand of active genes. Stalling of RNA polymerase II (RNAPII) at DNA lesions initiates TCR through the recruitment of the CSB and CSA proteins. The full repertoire of proteins required for human TCR - particularly in a chromatin context - remains to be determined. Studies in mice have revealed that the nucleosome-binding protein HMGN1 is required to enhance the repair of UV-induced lesions in transcribed genes. However, whether HMGN1 is required for human TCR remains unaddressed. Here, we show that knockout or knockdown of HMGN1, either alone or in combination with HMGN2, does not render human cells sensitive to UV light or Illudin S-induced transcription-blocking DNA lesions. Moreover, transcription restart after UV irradiation was not impaired in HMGN-deficient cells. In contrast, TCR-deficient cells were highly sensitive to DNA damage and failed to restart transcription. Furthermore, GFP-tagged HMGN1 was not recruited to sites of UV-induced DNA damage under conditions where GFP-CSB readily accumulated. In line with this, HMGN1 did not associate with the TCR complex, nor did TCR proteins require HMGN1 to associate with DNA damage-stalled RNAPII. Together, our findings suggest that HMGN1 and HMGN2 are not required for human TCR.
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PMID:Human HMGN1 and HMGN2 are not required for transcription-coupled DNA repair. 3215 97

The response to DNA damage-stalled RNA polymerase II (RNAPIIo) involves the assembly of the transcription-coupled repair (TCR) complex on actively transcribed strands. The function of the TCR proteins CSB, CSA and UVSSA and the manner in which the core DNA repair complex, including transcription factor IIH (TFIIH), is recruited are largely unknown. Here, we define the assembly mechanism of the TCR complex in human isogenic knockout cells. We show that TCR is initiated by RNAPIIo-bound CSB, which recruits CSA through a newly identified CSA-interaction motif (CIM). Once recruited, CSA facilitates the association of UVSSA with stalled RNAPIIo. Importantly, we find that UVSSA is the key factor that recruits the TFIIH complex in a manner that is stimulated by CSB and CSA. Together these findings identify a sequential and highly cooperative assembly mechanism of TCR proteins and reveal the mechanism for TFIIH recruitment to DNA damage-stalled RNAPIIo to initiate repair.
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PMID:The cooperative action of CSB, CSA, and UVSSA target TFIIH to DNA damage-stalled RNA polymerase II. 3315 85

Transcription elongation by RNA polymerase II (Pol II) is constantly challenged by numerous types of obstacles that lead to transcriptional pausing or stalling. These obstacles include DNA lesions, DNA epigenetic modifications, DNA binding proteins, and non-B form DNA structures. In particular, lesion-induced prolonged transcriptional blockage or stalling leads to genome instability, cellular dysfunction, and cell death. Transcription-coupled nucleotide excision repair (TC-NER) pathway is the first line of defense that detects and repairs these transcription-blocking DNA lesions. In this review, we will first summarize the recent research progress toward understanding the molecular basis of transcriptional pausing and stalling by different kinds of obstacles. We will then discuss new insights into Pol II-mediated lesion recognition and the roles of CSB in TC-NER.
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PMID:Molecular basis of transcriptional pausing, stalling, and transcription-coupled repair initiation. 3327 12


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