EXPRESSION, PHOSPHORYLATION AND NUCLEAR-LOCALIZATION OF THE HUMAN P1 PROTEIN, A HOMOLOG OF THE YEAST MCM-3 REPLICATION PROTEIN

The human protein P1 belongs to a newly discovered class of mammalian nuclear proteins with high sequence homology to yeast replication prot eins, We present the entire amino acid sequence of the human protein P 1 as predicted from the cDNA sequence, and show that P1 shares three c entral regions of high sequence similarity (about 75%) and a highly hy drophilic carboxy-terminal region with the yeast Mcm3 replication prot ein, The human genome most probably contains one P1 gene which is acti vated when HeLa cells progress to S phase, as shown by a several-fold increase in P1-specific mRNA, However, the amounts of P1 protein do no t detectably change during this period, but P1 protein becomes phospho rylated at the beginning of S phase, In contrast to the yeast Mcm prot eins, which disappear from nuclei after initiation of DNA replication, protein pi remains in the nucleus during and after S phase, pi is dis persed in mitotic cells and may be excluded from binding to chromosome s.