An evolutionarily conserved germ cell-specific hnRNP is encoded by a retrotransposed gene

The gene encoding heterogeneous ribonucleoprotein (hnRNP) G recently has be en mapped to the X chromosome. All mammals have a Y chromosome-encoded homo logue of HNRNP G called RBMY, which is implicated with a role in male ferti lity and is a candidate for the azoospermia factor gene. We have identified a new member of this gene family, HNRNP G-T, and have mapped it as a singl e-copy gene on chromosome 11, This gene contains an uninterrupted open read ing frame and no introns, consistent with derivation from a retroposon, How ever, unlike many retroposon-derived genes, HNRNP G-Tis not a pseudogene. A n antiserum raised to the conceptual reading frame of HNRNP G-T showed that it encodes a protein that is highly expressed in germ cells and in particu lar in the nuclei of meiotic spermatocytes, Surprisingly, although this ant iserum was raised against human hnRNP G-T protein, it can also detect a sim ilar protein in the testis of several mammals. This suggests that the prote in is highly conserved and that the retrotransposition event generating the HNRNP G-T gene predated at least the common ancestor of mouse and man. The existence of an additional testis-specific hnRNP a family member provides evidence for the importance of these proteins in normal germ cell developme nt.