The six minichromosome maintenance proteins (Mcm2-7) are required for both the 
initiation and elongation of chromosomal DNA, ensuring that DNA replication 
takes place once, and only once, during the S phase. Here we report on the 
cloning of a new human Mcm gene (hMcm8) and on characterisation of its protein 
product. The hMcm8 gene contains the central Mcm domain conserved in the Mcm2-7 
gene family, and is expressed in a range of cell lines and human tissues. hMcm8 
mRNA accumulates during G(1)/S phase, while hMcm8 protein is detectable 
throughout the cell cycle. Immunoprecipitation-based studies did not reveal any 
participation of hMcm8 in the Mcm3/5 and Mcm2/4/6/7 subcomplexes. hMcm8 
localises to the nucleus, although it is devoid of a nuclear localisation 
signal, suggesting that it binds to a nuclear protein. In the nucleus, the hMcm8 
structure-bound fraction is detectable in S, but not in G(2)/M, phase, as for 
hMcm3. However, unlike hMcm3, the hMcm8 structure-bound fraction is not 
detectable in G(1) phase. Overall, our data identify a new Mcm protein, which 
does not form part of the Mcm2-7 complex and which is only structure-bound 
during S phase, thus suggesting its specific role in DNA replication.