Expression, nuclear localization and interactions of human MCM/P1 proteins

We report here the comparative analysis of human Mcm/P1 proteins (HsMcm2, -3, -5 and -7), including a characterization of their mutual interactions, cell cycle dependent expression and nuclear localization during the cell cycle and the quiescent state. The mRNA levels of these genes, which undergo cell cycle dependent oscillations with a peak at G1/S phase, may be regulated by E2F motifs, two of which were detected in the 5' upstream region of the HsMCM5 gene, In contrast, the protein levels of these Mcm proteins were found to remain rather constant during the HeLa cell cycle, However, their levels gradually increased in a variable manner as KD cells progressed from G0 into the G1/S phase, In the G0 stage, the amounts of HsMcm2 and -5 proteins were much lower than those of HsMcm7 and -3 proteins, suggesting that they are not present in stoichiometric amounts, and that only a proportion of these molecules actively participate in cell cycle regulation as part of Mcm/P1 complexes. (C) 1997 Academic Press.