Identification of Cdc45p, an essential factor required for DNA replication.

CDC45 is an essential gene required for initiation of DNA replication in the budding yeast Saccharomyces cerevisiae. CDC45 interacts genetically with CDC46 and CDC47, both members of the MCM family of genes which have been implicated in the licensing of DNA replication. In this report, the isolation of CDC45 is described. The complementing gene is linked to an essential open reading frame on chromosome XII. CDC45 was found to be cell cycle regulated and steady-state mRNA levels are G1/S-specific. CDC45 encodes a protein structurally related to Tsd2p, a protein required for DNA replication in Ustilago maydis. CDC45 also interacts genetically with ORC2, the gene encoding the second subunit of the origin recognition complex, ORC, and MCM3, another member of the MCM family. The cdc45-1 mutant has a plasmid maintenance defect which is rescued by the addition of multiple potential origins to the plasmid.