FIG. 1.

(A) Alignment of protein sequences of hCdc18 (hscdc18) with those of hOrc1 (hsorc1), S. pombe Cdc18 (spcdc18), and S. cerevisiae CDC6 (sccdc6). The numbers refer to the sequence of hCdc18. The alignment was done with the PILEUP program of the Genetics Computer Group package. Identical amino acids are shaded. Arrows mark putative substrate sites for cyclin-cdk’s (on the hscdc18 protein), and the putative bipartite NLS is underlined. Conserved boxes 1 to 6 are indicated; boxes 1 and 3 contain the P and A loops, respectively. (B) Schematic representation of the hCdc18 protein divided into three domains. Boxes 1 to 6 in the middle one-third of the protein are the same as in panel A. S, a serine in a putative cyclin-cdk phosphorylation site; NLS, putative bipartite nuclear localization sequence; NTP, nucleoside triphosphate. The horizontal lines represent recombinant fragments of Cdc18 which are sufficient to mediate the interactions with Orc1, Cdc18 (Fig. 4A), and cyclin A (data not shown).