MULTIPLE FUNCTIONAL COPIES OF THE RBM GENE FAMILY, A SPERMATOGENESIS CANDIDATE ON THE HUMAN Y-CHROMOSOME

The RBM (RNA-binding motif) gene family on the human Y chromosome enco des proteins with an RNA-binding domain. Its exclusive expression in g erm cells and its partial deletion in some azoospermic or severely oli gospermic males provide evidence of a role for RBM genes in spermatoge nesis. There are approximately 30 RBM genes, found on both arms of the Y chromosome. Two RBM cDNA clones with slightly different sequences h ave been reported. To investigate the number of functional genes, we s tudied RBM expression by use of RT-PCR of RBM transcripts and by chara cterizing numerous RBM cDNA clones. A total of 27 RT-PCR and 19 cDNA c lones were sequenced. Whereas the RT-PCR clones pointed to the existen ce of at least six RBM subfamilies (RBMI to RBMVI), the cDNA clones in dicated that only RBMI is actively transcribed and encodes functional proteins. A total of six RBMI genes were identified, which produce fou r polypeptides due to some silent base substitutions. The transcripts of each gene are alternatively spliced to generate protein isoforms wi th three or four SRGY boxes, thus greatly increasing the complexity of the products of the RBM gene family. We also provide evidence suggest ing that a 5-bp deletion in a previously reported RBM cDNA clone repre sents a processing irregularity. (C) 1997 Academic Press.