Protein-protein interactions of Sid2p, a Saccharomyces cerevisiae protein required for DNA replication

SID2 is the S. cerevisiae ortholog of CDT1, an essential gene required for origin licensing in DNA replication. An allele of SID2, sid2-1, was originally identified in a screen for mutants synthetically lethal with deletion of Sic1, a Clb-Cdc28 kinase inhibitor. Here, field inversion gel electrophoresis conducted on chromosomes isolated from sid2-21 cells indicate that they arrest with replication forks or bubbles. A two hybrid library screen of protein-protein interactions involving both wild-type and mutant forms of Sid2p isolated many proteins that interact with Sid2p. However, this analysis appears to have failed to give insight into its biologically relevant interacting partners, as the proteins identified have a variety of functions. The S. pombe homologs of Sid2p and Cdc6p, Cdtlp and Cdc18p, have been shown to co-immunoprecipitate. However, a direct two hybrid test of physical interactions between Sid2p and Cdc6p indicate that Sid2p may function in a manner that does not involve physical interaction with Cdc6p. These results indicate that although SID2 is the S. cerevisiae ortholog of CDT1, the specific mechanisms underlying its role in DNA replication may diverge