SPECIAL MATHEMATICS COLLOQUIUM
Speaker: Mariel Vazquez
Abstract DNA replication is the mechanism by which a cell copies its genetic code prior to dividing into two daughter cells. DNA replication must produce two identical and independent copies of the parental DNA molecule(s). However, replication of circular DNA results in two topologically linked DNA circles. In this case, cell survival relies on removing this topological obstruction. An important example is that of the bacterium Escherichia coli whose genome is contained in a single circular chromosome. Until recently it was believed that enzymes called topoisomerases exclusively resolve replication links. However, the Sherrat lab showed that Xer recombinases can untie replication links (Grainge et al., 2007). We use the tangle method of Ernst and Sumners (1990) and other topological methods to show definitively that there is a unique shortest pathway of unlinking by Xer recombination that strictly reduces the complexity of the links at every step. We delineate the mechanism of action of the enzymes at each step along this pathway and provide a 3D interpretation of the results.