Examination of Replication Dynamics in Fragile Sites Through Molecular Combing

Chromosomal fragile sites are specific loci that exhibit instability visible as gaps and breaks on the chromosome following inhibition of DNA synthesis and are generally categorized into two main classes: rare fragile sites (RFSs) and common fragile sites (CFSs). Under standard conditions, CFSs are typically stable but are prone to breakage in cells subjected to replication stress. In recent years, their role in the generation of gross chromosome rearrangements has become increasingly evident, and fragile sites have now connected to chromosome instability in cancer cells. The connection between CFSs and cancer thus highlights the importance of the regulation of DNA replication to prevent cancer development. The study of fragile sites in the yeast model organism has provided insight into the mechanisms that lead to breakage and genome instability. Through the process of molecular combing, replication dynamics can be observed at fragile sites to further understand the consequence of replication stress on DNA damage

Analysis of gene conversion tracts in \u3ci\u3eSaccharomyces cerevisiae\u3c/i\u3e

Common fragile sites are regions of the genome prone to gaps and breakage under replication stress. Repair of breaks at CFS can occur through homologous recombination. yet may lead to loss of heterozygosity (LOH) events that manifest themselves as gene conversions. Gene conversions associated with LOH have the potential to deactivate tumor suppressor genes, driving tumor progression. Using the yeast model, Saccharomyces cerevisiae, evidence of two types of gene conversions has emerged: short-tract and long-tract gene conversions. Gene conversion maps show a high frequency of short-tract gene conversions ending near or at the SUP4-o tRNA, in yeast strain Y657 that contains SUP4-o. We hypothesized that termination of these tracts is due to replication fork pause sites created by SUP4-o. We find the 2% difference in frequency of terminations between Y657, and our experimental yeast strain that contains SUP4-o, AMC355, does not provide statistical support for our hypothesis of SUP4-o causing termination of gene conversion tracts. We see that gene conversions near SUP4-o vary in their tract length. These gene conversions have implications for possible LOH after repair at fragile sites and may contribute to cancer progression