Molecular Mechanism of Initiation of DNA Replication

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In the yeast Saccharomyces cerevisiae as well as other eukaryotic cells, Cdc7/Dbf4 protein kinase complex is required for intiation of chromosomal DNA replication. To elucidate the function of Cdc7/Dbf4 in the cell cycle the complex was expressed in insect cells and purified to its homogeniety. The purified complex specifically phosphorylated yeast Mcm2 protein in uttro, suggesting that one of in utuo targets of Cdc7/Dbf4 protein kinase is Mcm2-7 protein complex and this phosphorylation leads to functional change of Mcm2-7 protein complex during the cell cycle. McmlO protein is also known to be required for intiation of chromosomal DNA replication in S.cereuisiae. It has been shown that Mcm lOp physically interacts with ORC, Origin Recognition Complex, which bind at orgins thoughout the cell cycle and is also required for initiation of chromosomal DNA replication, suggesting that McmlOp plays as an anchor for the formation of initiation cornplex at chromosomal DNA replication origins i … More n S.cerevisiae. Schizosaccharomyces pombe cdc23^+ complimented the mcmlO mutations of S.cerevisiae, suggesting that Cdc23p is a functional homolog of McmlOp.The DPB11 gene, which genetically interacts with DNA polymerase II (epsilon), one of three replicative DNA polymerases is required for DNA replication and the S phase checkpoint in S.cerevistae. To identify factors interacting with Dpbllpwe have isolated sld (synthetically lethal with dpbll-1) mutations which fall into six complementation groups (sldl to -6). It has been found that SLD1 is identical to DPB3, which encodes the third subunit of DNA polymerase II holoenzyme SLD4 is the same as 0DC45, which is required for initiation of chrornsomal DNA replication, and SLD6 is identical to RAD53, which is required for DNA damage as wellas S phase checkpoint, while SLD2, -3, and -5 are newly identified genes. These newly identified gene products are also required for initiation of DNA replication. Thus, DNA polymerase II should play an crutial role during the intiation step of DNA replication as well as during the elongation step of chromsomal DNA replication in S, cerevisiae. Less