MCM3(MINICHROMOSOME MAINTENANCE, S. CEREVISIAE, HOMOLOG OF, 3),also called RLFB or P1 PROTEIN, is a protein that in humans is encoded by the MCM3 gene. MCM3 is one of the highly conserved mini-chromosome maintenance proteins (MCM) that are involved in the initiation of eukaryotic genome replication. The MCM3 gene is mapped to 6p12.2. This protein is a subunit of the protein complex that consists of MCM2-7. It has been shown to interact directly with MCM5/CDC46. This protein also interacts with, and thus is acetlyated by MCM3AP, a chromatin-associated acetyltransferase. The acetylation of this protein inhibits the initiation of DNA replication and cell cycle progression.