We have identified a cDNA encoding a 212 amino acid protein (Nm23-H5) with 27^31% identity to the human members of the nm23/nucleoside diphosphate (NDP) kinase gene family. The nm23-H5 gene is located on chromosome 5q23^31 and is transcribed as one main transcript of 1.1 kb which is highly and specifically expressed in testis, in the spermatogonia and early spermatocytes. Nm23-H5 possesses most of the residues conserved among NDP kinases plus an additional COOHterminus end of 55 amino acids unique to this protein. However, under usual assay conditions, Nm23-H5 expressed in Escherichia coli did not exhibit NDP kinase activity. These results suggest that Nm23-H5 is specifically involved in early stages of spermatogenesis.z 1998 Federation of European Biochemical Societies.

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