The Schizosaccharomyces pombe genes, nda1 and nda4, are essential for the normal regulation of DNA replication and belong to the MCM gene family. This gene family includes Saccharomyces cerevisiae MCM2, MCM3, MCM5/CDC46 and CDC47, S. pombe nda1, nda4, cdc21 and mis5, and genes encoding human BM28, P1MCM3 and P1.1MCM3 and mouse P1MCM3, most of which are considered to be required for the initiation of DNA replication. We isolated two homologues of the MCM genes, xMCM2 and xCDC46, from a Xenopus laevis cDNA library using the polymerase chain reaction (PCR) method. The predicted amino acid (aa) sequences of xMCM2 and xCDC46 are most similar to those of human BM28 (78% identity) and S. pombe Nda4 (48% identity), respectively. By Western blot analysis using anti-xMCM2 and anti-xCDC46 polyclonal antibodies (Ab) raised against glutathione S-transferase (GST)::xMCM2 or GST::xCDC46 fusion proteins, xMCM2 and xCDC46 were identified as 120- and 95-kDa proteins, respectively. When either xMCM2 or xCDC46 was immunoprecipitated with the specific Ab, the other was also co-precipitated. These results suggest that xMCM2 and xCDC46 physically interact with each other.