Browsing by keyword "DNA Topoisomerases, Type I"
Now showing items 1-2 of 2
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Inhibition of cytotoxic T lymphocyte-induced target cell DNA fragmentation, but not lysis, by inhibitors of DNA topoisomerases I and IICytotoxic T lymphocytes (CTL) kill their target cells via a contact-dependent mechanism that results in the perturbation of the target cell's plasma membrane and the fragmentation of the target cell's DNA into nucleosomal particles. The membrane disruption is presumed to be due to the action of perforin, while the DNA fragmentation is thought to be by the activation of an endogenous nuclease(s). DNA topoisomerases I and II are nuclear enzymes with inherent endonuclease activities. We have investigated their role in the CTL-induced DNA fragmentation process. We report that in CTL killing assays, the treatment of target cells with topoisomerase I and II inhibitors blocks the CTL-induced DNA fragmentation process, but not the lysis of the target cell.
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Patterns and mechanisms of ancestral histone protein inheritance in budding yeastReplicating chromatin involves disruption of histone-DNA contacts and subsequent reassembly of maternal histones on the new daughter genomes. In bulk, maternal histones are randomly segregated to the two daughters, but little is known about the fine details of this process: do maternal histones re-assemble at preferred locations or close to their original loci? Here, we use a recently developed method for swapping epitope tags to measure the disposition of ancestral histone H3 across the yeast genome over six generations. We find that ancestral H3 is preferentially retained at the 5' ends of most genes, with strongest retention at long, poorly transcribed genes. We recapitulate these observations with a quantitative model in which the majority of maternal histones are reincorporated within 400 bp of their pre-replication locus during replication, with replication-independent replacement and transcription-related retrograde nucleosome movement shaping the resulting distributions of ancestral histones. We find a key role for Topoisomerase I in retrograde histone movement during transcription, and we find that loss of Chromatin Assembly Factor-1 affects replication-independent turnover. Together, these results show that specific loci are enriched for histone proteins first synthesized several generations beforehand, and that maternal histones re-associate close to their original locations on daughter genomes after replication. Our findings further suggest that accumulation of ancestral histones could play a role in shaping histone modification patterns.
