Helicase Requirements for Prevention of Fragility at the Flex1 AT Repeat.
Regan, Samantha B.
- Common fragile sites are regions of the genome that are present in all individuals, and prone to breakage under replicative stress. FRA16D, one of the most highly expressed common fragile sites, is located in the WWOX gene. The WWOX protein is a putative tumor suppressor which has been linked to cancer proliferation. Flex1, an AT-rich sequence within the FRA16D site, contributes to much of FRA16D’... read mores fragility (Zhang and Freudenreich, 2007). It is possible that a secondary structure may form in Flex1, causing fragility. These secondary structures may need to be unwound, or they may stall replication and cause a reversed fork; either scenario can prevent proper replication progression and result in DNA breakage. In this project, genetic assays in Saccharomyces cerevisiae were used to indirectly measure fragility of Flex1 in the absence of various helicases associated with replication and DNA damage and repair. The rate of fragility in the presence and absence of helicases Rrm3, Srs2, Sgs1, and Mph1 was evaluated. The absence of Rrm3 seems to cause a decrease in fragility at Flex1. The presence of Sgs1 and Mph1 have a protective effect at Flex1, and in their absence there is an increase in fragility. Srs2 does not seem to have an effect fragility at Flex1. Based on these results, it is possible to predict that some of these helicases may prevent breakage at Flex1 through the formation of regressed forks (especially Mph1). Fork regression could lead to eventual fork restart or mitotic DNA synthesis across the AT repeat at Flex1, and be a way to avoid DNA fragility.read less