Massachusetts Institute of Technology, Department of Biology
Abstract: The assembly of replisomes at eukaryotic origins of replication is a complex process that is carefully coordinated with the cell cycle to ensure that the genome is replicated exactly once per cell cycle. During G1, two copies of the hexameric replicative DNA helicase, the Mcm2-7 complex, are loaded at each origin of replication as a head-to-head double hexamer. This conformation sets the stage for subsequent bidirectional replication. As cells enter S phase, these loaded helicases are selectively activated and replisomes are assembled around them. Helicase activation does not occur at the same time for each origin. Instead, origins initiate at characteristic times during S phase.
In the first part of my presentation, I will discuss how we have used single-molecule biochemical approaches to understand the mechanism of helicase loading. These studies have revealed aspects of this process that drive formation of the head-to-head double hexamer required for bidirectional initiation. In addition, I will discuss more recent studies that reveal how Mcm2-7 ring opening and closing are controlled during this process. The second part of my presentation will focus on our efforts to reconstitute in vitro replication initiation in the context of nucleosomal DNA templates. In particular, I will present data suggesting that the nature of the nucleosomal template can independently influence helicase loading or helicase activation. Intriguingly, I will discuss data that suggests that we have recapitulated characteristics of early- and late-initiating origins of replication in a fully-purified replication assay.
Friday, April 1, 2016
Host: Oscar Aparicio