Project description:UV-induced DNA lesions are an important contributor to mutagenesis and cancer, but it is not fully understood how the chromosomal landscape influences UV lesion formation and repair. We have used a novel high-throughput sequencing method to precisely map UV-induced cyclobutane pyrimidine dimers (CPDs) at nucleotide resolution throughout the yeast genome. Analysis of CPD formation reveals that nucleosomal DNA having an inward rotational setting is protected from CPD lesions. In strongly positioned nucleosomes, this nucleosome 'photofootprint' overrides intrinsic dipyrimidine sequence preferences for CPD formation. CPD formation is also inhibited by DNA-bound transcription factors, in effect protecting important DNA elements from UV damage. Analysis of CPD repair revealed a clear signature of efficient transcription-coupled nucleotide excision repair. Repair was less efficient at translational positions near a nucleosome dyad and at heterochromatic regions in the yeast genome. These findings define the roles of nucleosomes and transcription factors in UV damage formation and repair. UV mapping data was analyzed for yeast cells irradiated with 125J/m2 and allowed to repair for 0hr (2 samples), 20 minutes, 1 hour, or 2 hours. Data is also included for naked DNA irradiated with UV 60 or 90 J/m2
Project description:Elf1 is an important transcription elongation factor that has been implicated in transcription coupled-nucleotide excision repair (TC-NER). Here, we have used a high-throughput sequencing method known as CPD-seq to map the repair of UV-induced cyclobutane pyrimidine dimers (CPDs) at single nucleotide resolution across the yeast genome in elf1 mutant cells. Analysis of CPD repair indicates that Elf1 is important for CPD repair in the transcribed strand (TS) of yeast genes, indicating it plays an important role in TC-NER.
Project description:UV-induced DNA lesions are an important contributor to mutagenesis and cancer, but it is not fully understood how the chromosomal landscape influences UV lesion formation and repair. We have used a novel high-throughput sequencing method to precisely map UV-induced cyclobutane pyrimidine dimers (CPDs) at nucleotide resolution throughout the yeast genome. Analysis of CPD formation reveals that nucleosomal DNA having an inward rotational setting is protected from CPD lesions. In strongly positioned nucleosomes, this nucleosome 'photofootprint' overrides intrinsic dipyrimidine sequence preferences for CPD formation. CPD formation is also inhibited by DNA-bound transcription factors, in effect protecting important DNA elements from UV damage. Analysis of CPD repair revealed a clear signature of efficient transcription-coupled nucleotide excision repair. Repair was less efficient at translational positions near a nucleosome dyad and at heterochromatic regions in the yeast genome. These findings define the roles of nucleosomes and transcription factors in UV damage formation and repair.
Project description:Rad16 is required for global genomic nucleotide excision repair (GG-NER) of UV-induced CPD lesions. Here we have used a novel high-throughput sequencing method known as CPD-seq to map the repair of UV-induced cyclobutane pyrimidine dimers (CPDs) at single nucleotide resolution across the yeast genome in rad16 mutant cells. Analysis of CPD repair indicates that rad16 is generally required for CPD repair in the non-transcribed strand (NTS) of yeast genes and non-transcribed genomic regions.
Project description:Transcription-coupled nucleotide excision repair (TC-NER) is an important DNA repair mechanism that responds to RNA polymerase (RNAP) stalling and removes DNA lesions from transcribed genes. Activation of TC-NER requires specific factors, such as human Cockayne syndrome group B (CSB) protein or its yeast homolog Rad26. Mutations in CSB are associated with the severe neurological disorder Cockayne syndrome. However, the genome-wide role of CSB/Rad26 in TC-NER, particularly in the context of chromatin organization, is not fully understood. Here we used single-nucleotide resolution UV damage mapping data to investigate the genome-wide function of Rad26 in TC-NER. Our data shows that Rad26 is critical for TC-NER in transcribed regions downstream of the first (+1) nucleosome; however, Rad26 is largely dispensable for TC-NER in the +1 nucleosome. We further show that the Rad26-independent TC-NER in the +1 nucleosome is correlated with high occupancy of the transcription initiation/repair factor TFIIH. Downstream of the +1 nucleosome, the combination of low TFIIH occupancy and high occupancy of the transcription elongation factor Spt4/Spt5 suppresses TC-NER when Rad26 is dysfunctional. Deletion of SPT4 significantly restores TC-NER in the downstream nucleosomes in a rad26∆ mutant. Collectively, these data indicate that the requirement for Rad26 in TC-NER is modulated by the distribution of TFIIH and Spt4/Spt5, and Rad26 mainly functions in the downstream nucleosomes to remove TC-NER suppression by Spt4/Spt5.
Project description:Global Genomic Repair (GGR) and Transcription-Coupled Repair (TCR) have been viewed, respectively, as major and minor sub-pathways of the nucleotide excision repair (NER) process that removes bulky lesions from the genome. Here we applied a next generation sequencing assay, CPD-seq, in E. coli to measure the levels of cyclobutane pyrimidine dimer (CPD) lesions before, during, and after UV-induced genotoxic stress, and, therefore, to determine the rate of genomic recovery by NER at a single nucleotide resolution. We find that active transcription is necessary for the repair of not only the template strand (TS), but also the non-template strand (NTS), and that the bulk of TCR is independent of Mfd – a DNA translocase that is thought to be necessary and sufficient for TCR in bacteria. We further show that repair of both TS and NTS is enhanced by increased readthrough past Rho-dependent terminators. We demonstrate that UV-induced genotoxic stress promotes global antitermination so that TCR is more accessible to the antisense, intergenic, and other low transcribed regions. Overall, our data suggests that GGR and TCR are essentially the same process required for complete repair of the bacterial genome.
Project description:Repair of UV damage from the transcribed strand (TS) of yeast genes is rapid due to the transcription coupled nucleotide excision repair (TC-NER) pathway. TC-NER is triggered when RNA polymerase stalls at UV damage, such as a UV-induced cyclobutane pyrimidine dimer (CPD). During transcription, the histone methyltransferase Set2 methylates histone H3K36, but it is not known if Set2 regulates TC-NER. Here, we report genome-wide repair maps of UV-induced cyclobutane pyrimidine dimers (CPDs) in yeast cells lacking Set2.
Project description:We characterized the role of H3K36 methylation in regulating repair of UV damage from the transcribed strand (TS) of yeast genes by the transcription coupled nucleotide excision repair (TC-NER) pathway. TC-NER is triggered when RNA polymerase stalls at UV damage, such as a UV-induced cyclobutane pyrimidine dimer (CPD). During transcription, the histone methyltransferase Set2 methylates histone H3K36, but it is not known if H3K36 methylation regulates TC-NER. Here, we report genome-wide repair maps of UV-induced cyclobutane pyrimidine dimers (CPDs) in yeast cells containing mutants in histone H3K36 (or set2).