Again, very high levels of damage were generated by irradiating yeast cells with a UV dose of 10,000 J/m2

Again, very high levels of damage were generated by irradiating yeast cells with a UV dose of 10,000 J/m2. contexts than can be readily assessed using previous methods. Recent efforts to develop whole genome maps of DNA damage, repair processes, and even mutations promise to greatly expand our understanding of DNA repair and mutagenesis. Here we review the current efforts to utilize whole genome maps of DNA damage and mutation to understand how different chromosomal contexts impact DNA excision repair pathways. substrates Inolitazone dihydrochloride to measure repair activity [2]. Inolitazone dihydrochloride These methods have been extremely useful for deciphering repair pathways and activities within cells. However, measuring repair of bulk Rabbit Polyclonal to ANKK1 DNA or repair at selected loci does not fully capture the range of genomic and chromatin contexts that this repair machinery must grapple with gene, which is required for NER, eliminated CPD removal in the nuclear genome. The authors observed wide variations in CPD repair rates across the yeast genome, yet the underlying cause(s) of this variance are unclear. 2.2. Mapping UV damage frequency and repair in the human genome A similar method has been Inolitazone dihydrochloride used to map UV-induced CPD lesions in the human genome [24]. In this study, Zavala et al. used tiling microarrays to map CPD damage along human chromosomes 1 and 6, comprising ~400 Mbp of genomic sequence. These microarrays experienced a considerably higher density of probes than the yeast study, with an average probe-to-probe spacing of 35 bp. This high resolution enabled the authors to identify and characterize CPD hotspots, which were defined as regions with high levels of CPD lesions ( 3-fold enrichment relative to input and to IP transmission from undamaged cells). The authors mapped CPD lesions in immortalized human fibroblasts immediately following exposure to 12 J/m2 dose of UV radiation. This analysis recognized 1128 and 611 CPD hotspots on chromosome 1 and 6, respectively [24]. Intriguingly, the authors found that the distribution of CPD hotspots is not random, but instead is usually significantly associated with certain genomic features. For example, a high frequency of CPD hotspots are found among the histone gene clusters on chromosomes 1 (1q21) and 6 (6p21). The strongest association, however, was observed with short interspersed elements (SINE). These repetitive elements are an abundant feature of the human genome [26], but probes representing SINE sequences were not included on the microarray (likely to avoid artifacts due to cross-hybridization). Intriguingly, ~70% of the CPD hotspots abutted an Alu SINE, a frequency more than 10-fold higher than expected by random chance [24]. Because the CPD hotspots were derived from microarray probes covering unique sequences flanking each Alu element, this association is usually unlikely to be a microarray hybridization artifact due to the high copy number of repeat sequences. Instead, it appears that CPD hotspots preferentially form at many Alu SINEs in the human genome. Alu SINEs possess a quantity of distinguishing sequence features, including frequently a long polyA tract that is thought to be a remnant of the process of retrotransposition [26]. The long polyT tract around the complementary strand should be a high-frequency target for CPD lesions. Indeed, the authors found that many CPD hotspots were immediately adjacent to polyT tracts within Alu elements, suggesting a potential mechanism for CPD hotspot formation. Long polyA:T tracts also disfavor nucleosome formation [27C29], and thus damage in such regions could be more easily acknowledged and repaired by the NER machinery. It is interesting to speculate that polyA:T tracts in Alu elements and other repeat sequences could potentially function as a genomic sink for UV damage, in a sequence context in which the damage could be readily acknowledged and repaired. A separate study [25] used a similar approach to map CPD lesions for a small region of the human genome (10 Mbp of human chromosome 17). It was not reported whether high levels of CPD lesions were associated with Alu repeats. Importantly, this study also mapped the locations of cisplatin (or oxaliplatin) DNA adducts, thus demonstrating that this immunoprecipitation and microarray-based method can be used to map other classes of DNA lesions. 2.3. Modulation of chromatin structure during DNA repair Although these studies.