Initiation of DNA replication in eukaryotes is a tightly regulated process to ensure that the genome is replicated only once and at the proper time in the cell cycle. During initiation, a large number of proteins are mobilized to assemble at origins of replication, unwind the DNA duplex, and assemble into the functional replisome--the multiprotein machinery necessary to synthesize DNA at the replication fork. However, the specific functions and physical properties of many of these proteins, and thus the molecular mechanism of replication initiation, are unknown.  Studies using Xenopus extracts have shown that Mcm10 is one of the first proteins to associate with pre-replicative complexes at replication origins at the onset of S-phase, and is required for subsequent loading of downstream factors onto chromatin, including the helicase co-factor Cdc45. In order to gain a mechanistic understanding of Mcm10?s precise role, we are characterizing the structure and biochemical properties of vertebrate Mcm10. Here, we report the crystal structure of a highly conserved region of Mcm10 from Xenopus laevis. The structure shows two classic DNA binding motifs indicative of both single-stranded (ss) and double-stranded (ds) DNA binding. Crystallographic and biochemical analyses provide a model for how Mcm10 engages ss- and dsDNA at discrete but adjacent sites on the protein. These data suggest that Mcm10 might play a role in melting origin DNA and might preferentially associate with an emerging replication fork.