The replication licensing factor limits DNA replication to once in a cell cycle and is thought to contain MCM proteins as its component parts. Six MCM subtypes have been identified in various species. These MCM proteins are thought to bind each other to make a heteromeric complex. The Nda4 protein of Schizosaccharomyces pombe is one of the MCM proteins and is involved in DNA replication. The suppressor mutant of nda4 was isolated and the mutant gene was named sna41. The sna41-912 mutant demonstrated the ts phenotype, with an elongated cell shape at the restrictive temperature. Cells with 1C DNA content accumulated 2 h after shifting up to the restrictive temperature. This result suggests that sna41 is also involved in DNA replication. The sna41 genomic clone was isolated by a complementation of the ts phenotype of the mutant strain and was sequenced. The sna41 gene encodes a protein of 638 amino acids, which has low homology with CDC45 in S. cerevisiae. The gene disruption analysis showed that sna41 gene is essential for viability. The S. pombe sna41 mutation suppresses the nda4-108 mutation. Sna41 is involved in DNA replication and may play some roles in the regulation of DNA replication by the MCM proteins.