Background: The members of the MCM protein family, including MCM2, MCM3, Cdc21, CDC46, Mis5 and CDC47, are considered to be involved in the control of a single round of DNA replication during S phase in eukaryotes. They bind to chromatin during G1 and detach from it during S phase as if they license the chromatin to replicate. However, unlike the originally proposed 'licensing factor' and the budding yeast homologues, mammalian MCM2 and P1MCM3 proteins appeared to be localized in the nucleus during the interphase.