A NEW HUMAN NM23 HOMOLOG (NM23-H5) SPECIFICALLY EXPRESSED IN TESTIS GERMINAL CELLS

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 dipho sphate (NDP) kinase gene family. The nm23-H5 gene is located on chromo some 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 conser ved among NDP kinases plus an additional COOH-terminus 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 activ ity. These results suggest that Nm23-H5 is specifically involved in ea rly stages of spermatogenesis. (C) 1998 Federation of European Biochem ical Societies.