Essential and non-essential helicases maintain genome stability in Schizosaccharomyces pombe

2014-01-14A healthy cell needs to accurately duplicate its genome and pass one copy to each of its daughter cells. The DNA double helix is accessed by replication machinery once per cell cycle during S phase and regulated unwinding of this molecule is essential for replication. However, unwinding can make the DNA vulnerable to damage or breakage. Therefore, the process of unwinding must be carefully regulated. ❧ The conserved proteins Mcm2-7 form the MCM complex, which is the replicative helicase responsible for unwinding the DNA duplex during replication. The MCM complex also plays an important role in replication fork establishment. During S phase, replication fork stability is challenged by many natural impediments or environmental stresses, and control of the unwinding is essential to prevent fork collapse and DNA damage. The focus of my thesis is to gain deeper understanding of how helicase activities are regulated to preserve replication fork integrity. ❧ In chapter 2, I investigate a new factor that regulates the essential replicative helicase, MCM complex. Mcb1 is the ortholog of human MCM binding protein in S. pombe, and I found that Mcb1 antagonizes MCM helicase function by disrupting the association of Mcm2 with other MCM proteins. ❧ In chapter 3, I examined another conserved but non-essential helicase, Rad8. I investigated whether Rad8’s fork regression helicase domain is involved in replication fork restart during HU treatment. Using a genetic approach, I demonstrated that the ubiquitin ligase domain instead of helicase domain is required for Rad8 to promote fork recovery