From a human fetal-lung cDNA library, we isolated a gene, human MCM2, whose nucleotide sequence predicts a protein product homologous to the yeast nuclear proteins MCM2, MCM3, CDC21, and CDC46. Determination of cDNA sequences covering the entire coding region demonstrated an open reading frame of 1,629 nucleotides encoding 543 amino acids. Sequence comparison revealed 30-40% amino acid identity with these four yeast proteins, all of which are considered to play important roles in DNA replication. Analysis by Northern blotting revealed that the human MCM2 gene is expressed ubiquitously in normal tissues. Furthermore, we localized this gene to chromosomal bands 7q21.3-->q22.1 by fluorescence in situ hybridization.