PROPERTIES OF THE HUMAN NUCLEAR-PROTEIN P85MCM - EXPRESSION, NUCLEAR-LOCALIZATION AND INTERACTION WITH OTHER MCM PROTEINS

Recently we identified a cDNA fragment encoding a conserved part of a new human minichromosome maintenance (Mcm) protein, provisionally term ed P1.1Mcm3. Here, we report that the protein is most highly related t o a yeast cell-division-cycle protein, Cdc47, encoded by the open read ing frame YBR1441 on chromosome II of Saccharomyces cerevisiae. The hu man protein migrates on a polyacrylamide gel with an apparent molecula r mass of 85 kDa and shares areas of significant similarity with the M cm family of replication proteins. It is, therefore, designated as p85 Mcm. Microscopic immune-fluorescence studies revealed that protein p85 Mcm is located in the nuclei of interphase cells, but is evenly distri buted throughout the cell during mitosis. The amounts of p85Mcm do not significantly change during the cell cycle, but mRNA levels rise with the beginning of the S phase. However, in vitro, differentiation of H L60 cells results in a striking decrease of both p85Mcm mRNA and prote in levels, suggesting a role for p85Mcm in proliferating, but not in d ifferentiated cells. Under physiological salt conditions, p85Mcm is a component of a high molecular-mass complex including other Mcm protein s. The complex dissociates at high ionic strength given rise to stable subcomplexes, one of which contains protein p85Mcm together with Mcm proteins hCdc21 and p105Mcm.