Background: MCM-BP is a novel binding partner of the MCM complex; the mechanisms by which MCM-BP functions and associates with MCM complexes are not well understood. Results: Genetic analysis showed that mcb1 ts mutants exercise defective regulation of prereplicative MCM complex formation during DNA replication. Conclusion:Mcb1 regulates MCM function during prereplicative complex formation in DNA replication. Significance: This study presents the first evidence of MCM-BP function during prereplicative complex formation.