Anti-Human MCM4 (internal) Polyclonal antibody

MCM proteins are a conserved family of eukaryotic replication factors implicated in the initiation of DNA replication and in the discrimination between replicated and unreplicated chromatin, However, most mcm mutants in yeast arrest the cell cycle after bulk DNA synthesis has occurred. We investigated the basis for this late S phase arrest by analyzing the effects of a temperature-sensitive mutation in fission yeast cdc19(+) (mcm2(+)). cdc19-P1 cells show a dramatic loss of viability at the restrictive temperature, which is not typical of all S phase mutants. The cdc19-P1 cell cycle arrest requires an intact damage-response checkpoint and is accompanied by increased rates of chromosome loss and mitotic recombination. Chromosomes from cdc19-P1 cells migrate aberrantly in pulsed-field gels, typical of strains arrested with unresolved replication intermediates. The cdc19-P1 mutation reduces the level of the Cdc19 protein at all temperatures. We compared the effects of disruptions of cdc19(+) (mcm2(+)), cdc21(+) (mcm4(+)), nda4(+) (mcm5(+)) and mis5(+) (mcm6(+)); in all cases, the null mutants underwent delayed S phase but were unable to proceed through the cell cycle. Examination of protein levels suggests that this delayed S phase reflects limiting, but not absent, MCM proteins. Thus, reduced dosage of MCM proteins allows replication initiation, but is insufficient for completion of S phase and cell cycle progression.

We recently isolated a hypomorphic mutation of Mcm4 in a phenotype - based screen for chromosome instability in mice. This mutation, named Chaos3 ((c) under bar hromosome (c) under bar berrations (o) under bar ccurring (s) under bar pontaneously 3), causes exclusively mammary adenocarcinomas in similar to 80% of homozygous females. Mcm4 encodes a subunit of the MCM2-7 complex, the replication - licensing factor and the replicative helicase. The Mcm4(Chaos3) mutation appears to destabilize the MCM2-7 complex, causing impaired DNA replication. These findings demonstrate, for the first time, the causative role of an Mcm mutation in cancer development. Furthermore, this raises the possibility that hypomorphic mutations in MCM2-7 genes may increase breast cancer risk in humans.