ANALYSIS OF THE CDNA AND ENCODED PROTEIN OF THE HUMAN TESTIS-SPECIFICPGK-2 GENE

Because of their unique function, germ cells require unique gene produ cts. Thus, although the glycolytic enzyme phosphoglycerate kinase (PGK ) is required in all metabolically active cell types, there are two fu nctional PGK genes in the mammalian genome, one, PGK-1, that is X-link ed and ubiquitously expressed in all somatic tissues, and a second, PG K-2, that is autosomal and expressed only in spermatogenic cells. Expr ession of the PGK-2 gene may function solely to compensate for repress ed expression of the PGK-1 gene due to X-chromosome inactivation in sp ermatocytes. Alternatively, the PGK-2 gene could encode an isozyme wit h unique characteristics that are beneficial to spermatozoa. We have i solated a cDNA of the human PGK-2 gene and used this as probe to demon strate that transcription of this gene in spermatocytes and spermatids coincides with a period of repressed transcription of the X-linked PG K-I gene during spermatogenesis in the human testis. We have also anal yzed the amino acid sequence and protein characteristics of the PGK-2 isozyme deduced from this cDNA and compared them with that of the huma n PGK-1 isozyme to show that known structural and functional motifs ar e conserved in both proteins. Finally, we have examined the distributi on of the PGK-1 and PGK-2 isozymes during spermatogenesis in the mouse to show that while the PGK-2 protein does not appear to possess any u nique intracellular localization signal, it is more stable in vivo tha n the PGK-1 protein. (C) 1996 Wiley-Liss, Inc.