We have isolated a novel human cDNA that encodes a protein homologous to murine H5 and Diff6, and to yeast CDC10, and mapped it to chromosome region 2q37 by fluorescent in situ hybridization. Its transcript has an open reading frame of 1,218 nucleotides encoding 406 amino acids. The deduced peptide sequence contained conserved domains rich in basic residues, GXXGXGKS--DXXG--TKXD, a motif of the GTPase superfamily. Different polyA sites accounted for generation of two transcripts. The major type, 3.5 kb long, was expressed ubiquitously in all human tissues examined, but a 2.0-kb alternative transcript lacking any long AU-rich element in the 3' non-coding region was expressed abundantly only in testis, heart and skeletal muscle.