Regulation of Replication Origin Usage in Saccharomyces cerevisiae

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Coordination of DMA replication and gene expression is central to the regulation of cell proliferation. A strategy for the coordination of these two processes is to engage the same regulators in both processes. Classical examples of such dual functional regulators are the E. coll DnaA and the SV40 large T antigen, which serve both the functions of regulators of replication initiation and gene expression. Mcm1 is a MADS box transcription factor which regulates genes required for cell cycle progression and DMA replication. Its activity is responsive to glycolytic flux, nutrient availability and environmental stresses. Mcm1 also binds specific elements at replication origins to promote initiation of DMA replication. In this proposal, a direct role for Mcm1 in the regulation of origin usage is investigated. The hypothesis that Mcm1 regulates origin usage based on its occupancy under limiting conditions will be investigated at a genomic scale using three different approaches: 1) to exhaustively isolate autonomously replicating sequences that are selectively propagated, 2) to analyze the genome wide locations of Mcm1 at selected replication origins, 3) to identify differentially activated early replicating chromosomal origins. Dependence of the recruitment/activation of the pre-replication complex (pre-RC) on Mcm1 will be investigated by chromatin immunoprecipitation experiments. Interactions between Mcm1 and components of the pre-RC will be analyzed by electrophoretic mobility shift assay (EMSA) and Dnase! footprinting. Influence of Mcm1 on the local DMA and chromatin structures will be visualized by atomic force microscopy, electron microscopy as well as nucleosome mapping. Emerging examples of dual functional regulators that coordinate DMA replication and gene expression during cell proliferation include E2F-RB and Myb-130. Modeling this strategy in yeast may provide insights into the mechanistic actions of cell proliferation factors and tumor suppressors. Mis-regulated DNA replication is known to have adverse effects ranging from uncontrolled cell proliferation to cellular senescence. Uncoordinated DNA replication has also been linked to defects in chromosome condensation, cohesion and fragmentation, all of which have dire consequences on genome integrity. Therefore, understanding the regulation of DNA replication is central to the study of the etiology of all genetic diseases rooted in genome instability including trisomy and cancer.