MCM4(MINICHROMOSOME MAINTENANCE, S. CEREVISIAE, HOMOLOG OF, 4),also called CDC21, S. POMBE, HOMOLOG OF, is a protein that in humans is encoded by the MCM4 gene. MCM4 is one of the highly conserved mini-chromosome maintenance proteins (MCM) that are essential for the initiation of eukaryotic genome replication. The MCM4 gene is mapped to 8q11.21. The 864-amino acid MCM4 protein has an observed molecular mass of 97 kD by SDS-PAGE, which is similar to its calculated molecular mass of 96.6 kD. Western blot analysis with and without phosphatase treatment suggested that MCM4 is highly phosphorylated in mitotic cells. In the absence of DDK, CDK phosphorylation at the distal part of the Mcm4 NSD becomes crucial.MCM4 encodes a subunit of the MCM2-7 complex (also known as MCM2-MCM7), the replication licensing factor and presumptive replicative helicase.