Single-molecule Studies of Replicative DNA Helicases
DNA helicase, which separates the double helix into its component strands so they can be copied.In this talk, I will discuss our efforts to decipher the molecular mechanisms of two helicases: the MCM2-7 complex that acts as the replicative helicase in eukaryotes, and large T antigen (T-ag), the replicative helicase of Simian Virus 40 that serves as a paradigm for eukaryotic replication. Despite decades of study, the basic mechanisms by which these helicases unwind DNA at the replication fork have been controversial. Both enzymes were proposed to function as a physically coupled pair of hexamers that pumps double-stranded DNA through the helicase central channel, splitting the duplex apart when it emerges from the protein complex. Others challenged this view and proposed that they function as single hexamers that encircle and translocate along a single strand and unwind DNA by excluding the other strand from the central channel (“steric exclusion”).
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