A mammalian germ cell-specific RNA-binding protein interacts with ubiquitously expressed proteins involved in splice site selection

RNA-binding motif (RBM) genes are found on all mammalian Y chromosomes and are implicated in spermatogenesis, Within human germ cells, RBM protein sho ws a similar nuclear distribution to components of the pre-mRNA splicing ma chinery, To address the function of RBM, we have used protein-protein inter action assays to test for possible physical interactions between these prot eins. We find that RBM protein directly interacts with members of the SR fa mily of splicing factors and, in addition, strongly interacts with itself. We have mapped the protein domains responsible for mediating these interact ions and expressed the mouse RBM interaction region as a bacterial fusion p rotein. This fusion protein can pull-down several functionally active SR pr otein species from cell extracts. Depletion and add-back experiments indica te that these SR proteins are the only splicing factors bound by RBM which are required for the splicing of a panel of pre-mRNAs, Our results suggest that RBM protein is an evolutionarily conserved mammalian splicing regulato r which operates as a germ cell-specific cofactor for more ubiquitously exp ressed pre-mRNA splicing activators.