Modulation of DNA Synthesis in Saccharomyces cerevisiae Nuclear Extract by DNA Polymerases and the Origin Recognition Complex

We have analyzed the modulation of DNA synthesis on a supercoiled plasmid DNA template by DNA polymerases (pol), minichromosome maintenance protein complex (Mcm), topoisomerases, and the origin recognition complex (ORC) using an in vitro assay system. Antisera specific against the four-subunit pol α, the catalytic subunit of pol δ, and the Mcm467 complex each inhibited DNA synthesis. However, DNA synthesis in this system appeared to be independent of polϵ. Consequently, DNA synthesis in the in vitro system appeared to depend only on two polymerases, α and δ, as well as the Mcm467 DNA helicase. This system requires supercoiled plasmid DNA template and DNA synthesis absolutely required DNA topoisomerase I. In addition, we also report here a novel finding that purified recombinant six subunit ORC significantly stimulated the DNA synthesis on a supercoiled plasmid DNA template containing an autonomously replicating sequence, ARS1.