Mcm10 plays a key role in initiation and elongation of eukaryotic chromosomal DNA replication. As a first step to better understand the structure and function of vertebrate Mcm10, we have determined the structural architecture of Xenopus laevis Mcm10 (xMcm10) and characterized each domain biochemically. Limited proteolytic digestion of the full-length protein revealed amino-terminal (NTD), internal (ID), and carboxy-terminal (CTD) structured domains. Analytical ultracentrifugation revealed that xMcm10 self-associates and that the NTD forms homodimeric assemblies. DNA binding activity of xMcm10 was mapped to the ID and CTD, each of which binds to single- (ss) and double-stranded (ds) DNA with low micromolar affinity. The structural integrity of xMcm10-ID and CTD is dependent on the presence of bound zinc, which was experimentally verified by atomic absorption spectroscopy and proteolysis protection assays. The ID and CTD also bind independently to the amino-terminal 323 residues of the p180 subunit of DNA polymerase a-primase (pol a). We propose that the modularity of the protein architecture, with discrete domains for dimerization and for binding to DNA and pol a, provides an effective means for coordinating the biochemical activities of Mcm10 within the replisome.