n previous studies of DNA replication in drosophila ovary follicle cells we discovered a new complex thairegulates both gene expression and DNA replication in many cell types. This MMB/Dream complex remainsone major focus for continued study for us during the next period of this project. The complex containsmultiple DNA binding activities including an MJ hook in the core protein Mip 130 and specific DNA bindingfunctions in Mip 120, Myb and E2f2/DP/Rb proteins. We propose experiments to explore how this complexmay work to either repress or activate proximal origins of DNA replication or promoters for gene expressionin one cell type and in a developmental setting switch signs for activity at discrete locations. How thedifferent DNA binding factors touch DNA at different sites will be explored. One over-arching hypothesis tobe tested is that post-translational protein modifications (PTMs) mediated.by signalling kinases, otherproximal site-specific DNA factors and MMB composition together sen/e as ancf/or logic gates for function.Another hypothesis to be tested is that the precise structure and composition of the MMB nucleoproteincomplex at discrete sites is critical for function. Furthermore we will test the notion that ancillary factors thatrecognize histone modifications are targeted to specific loci by the MMB and that histone tail interactions arecritical for the decision for either repression or activation of a replication ori or a promoter. Integration of chromatin structure as mediated by complexes such as the MMB/Dream with therecruitment of proteins required for the basic function of a replication origin is another goal of this project.The MCM2-7 proteins ofthe eukaryote DNA replication machinery are recruited first as a pre-helicase to thepre-replication sites by concerted action of the six subunit ORC with CDC6 and Ctd-1. We will probe thestructure and function of ORC together with Cdc6 and ask if such complexes may distort DNA for the loadingof this inactive helicase. Activation of helicase activity requires the association of the GINS and Cdc 45proteins to such pre-replication complexes creating the active CMG complex. We will study the structure andfunction ofthe CMG helicase and explore the roles of PTMs mediated by the Cdc7/Dbf4 kinase in linking theCMG to functional replisomes.
The replication of DNA is a central step in the cell cycle and our work on the regulation and mechanisms ofthis process has uncovered'new protein complexes that are key factors widely conserved throughoutmulticellular animals including humans. Cancer and other proliferative diseases initiate with cellular eventsthat transform and release normal cell cycle controls. The signaling events that control the action ofreplication proteins, will be provide insights into the networks that control cell cycle progression and shouldhelp in cancer therapy and diagnosis.
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