Characterization of Cdc7 functional domains

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The cell division process is tightly regulated and closely coordinated with copying of its genetic material (DNA). Derangement of this process can be fatal or result in genetic instability. Protein kinase known as Cdc7 plays a critical role in this regulation by connecting the cell cycle engine (i.e., cyclin-dependent kinase) and the replication machinery (i.e., the enzymes copying DNA). To perform its function, Cdc7 must enter the nucleus and then bind to chromatin (i.e., DNA) where DNA replication starts. By mutation analysis, we previously found that the amino acid segment 203-370 contains the signal for the Cdc7 nuclear import. We also found that the segment 306-326 contained a signal for the Cdc7 nuclear retention, probably by binding to chromatin where new DNA synthesis begins. This nuclear retention signal is apparently antagonized by two small segments at the carboxyl terminus of Cdc7 protein, which we collectively term a nuclear export sequence. At present, we do not know: (a) if the signals for the nuclear import and retention are one integrated or two separate elements; (b) how the 21-amino acid segment (306-326) of the nuclear retention sequence regulates the interaction of Cdc7 with DNA (by which DNA synthesis may be activated or inactivated); and (c) how the amino acid modifications of Cdc7 is involved in the regulation of Cdc7 interactions with chromatin. We here propose to carry out an in-depth study of Cdc7 protein domains and critical amino acid residues within each domain. Data from this work will shed important new light on the regulation of DNA replication, and will help to unravelling the regulation mechanism as to how a cell maintains genetic stability.