Using cDNA selection with a YAC from the Xp11.2 region, we have identified a novel gene (RBM3) that encodes a polypeptide with high sequence similarity to a group of proteins that bind to RNA. On a YAC contig map, RBM3 is located between OATL1 and GATA1/TFE3 in sub-band Xp11.23, and gives rise to alternatively spliced transcripts in a variety of human tissues. The longest open reading frame encodes a 157 amino acid protein with a predicted molecular weight of 17 kDa. Its putative RNA-binding domain most closely resembles that of two previously characterized human RNA-binding proteins, YRRM, the gene for which has been implicated in azoospermia, and hnRNP G, a glycoprotein, also identified as an auto-antigen. The homology of RMB3 in both sequence and size to an RNA binding protein from maize, AAIP , suggests that it functions in a fundamental pathway conserved from plants to mammals.