Prerequisite for design of cancer therapy is the knowledge of cell growth control. The long term goal of this proposal is to understand the molecular mechanisms that control the two sequential and interdependent events of the cell cycle, i.e. DNA replication and mitosis. The research outlined here uses fission yeast, S. pombe, as a model system and addresses the mechanisms regulating the expression of DNA replicative proteins: if expression is altered what will the effects on cell division and cell growth be. The initial phase of the study is to obtain reagents and background information. Experiments to achieve these objectives are: (1) Isolation and characterization of the genes of S. pombe DNA polymerase a catalytic polypeptide and its p7O subunit, and the genes of DNA polymerase delta large subunit and its auxiliary protein PCNA. (2) Production of antibodies against these two S. pombe DNA polymerases and their associated proteins. (3) Investigation of gene expression of fission yeast DNA polymerases and their associated proteins at the transcriptional and translational levels, and posttranslational modification of the two DNA polymerases during the cell cycle. Fission yeast is the best studied mitotic control system among eukaryotes, but little is known about its regulatory mechanisms of DNA replication and the interdependent relationship of replication and mitosis. In mammalian cells, the lagging strand DNA polymerase, but postranslationally pol alpha, is constitutively expressed during the cell cycle, phosphorylated in a cell cycle-dependent manner by the key mitotic regulator p34(cdc2) associated kinase. After the initial phase of the study, we will: (1) identify the cell cycle-dependent posttranslationally modified residues and mutagenize these residues; (2) test the phenotype of these mutants during the cell cycle by disruption of the fission yeast gene followed by complementation with a mutagenized gene; (3) construct conditional lethal mutants for isolation of suppressors. These studies will provide novel information about the regulatory mechanisms of the leading and lagging strand DNA polymerases during cell growth, and pave the way for studying how cells modulate the order of DNA replication and cell division. Understanding of these fundamental mechanisms regulating cell growth and division will provide valuable inferences to molecular etiology in cancer therapies.
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