Eukaryotic DNA replication is mediated by a complex machinery consisting of several dozen proteins that ensures precise duplication of chromosomes in S phase of the cell cycle. The Diffley laboratory recently reconstituted the core Saccharomyces cerevisiae replication machinery in vitro from 19 replication factors containing about 50 individual protein subunits. This system allowed to study mechanisms of yeast MCM loading onto DNA and of yeast CMG replicative helicase activation. In human cells however, the process of replication initiation and its regulation are less well understood. In particular, the firing factors that activate the CMG helicase differ in domain composition and phospho-regulation from the yeast orthologs. Mechanistic studies are required to understand how human DNA replication is initiated and regulated at the molecular level. I will first reconstitute human DNA replication in vitro from completely recombinant components using methodology that I developed during my PhD. I will then use this system to study how the human replicative helicase is activated on the molecular level and how activation is regulated by phosphorylation using biochemistry. I will use cryo-electron microscopy (cryo-EM) to study the architecture of complexes involved in replication initiation. The reconstituted human system could in future enable studies on disease mechanisms and could allow screening for antiproliferative small molecule inhibitors.
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