NUCLEOTIDE-DEPENDENT PREREPLICATIVE COMPLEX ASSEMBLY BY CDC6P, A HOMOLOG OF EUKARYOTIC AND PROKARYOTIC CLAMP-LOADERS

Expression of the Cdc6 protein (Cdc6p) is essential for formation of p rereplicative complexes at budding yeast replication origins. Analysis of mutations in the conserved nucleoside triphosphate (NTP)-binding s ite of Cdc6p described here suggests that NTPs are required both for t he productive interaction of Cdc6p with replication origins during G1 and the quantitative loading of the Mcm2-7 family of proteins onto chr omatin. We show that Cdc6p exhibits significant sequence similarity to subunits of eukaryotic and prokaryotic clamp-loaders, which load ring -shaped DNA polymerase processivity factors onto DNA in an analogous r eaction. Similarities in both sequence and mechanism suggest that Cdc6 p and the clamp-loaders are members of a superfamily of nucleotide-dep endent loading factors.