AN H-YDB EPITOPE IS ENCODED BY A NOVEL MOUSE Y-CHROMOSOME GENE

Rejection of male tissue grafts by genotypically identical female mice has been explained by the existence of a male-specific transplantatio n antigen, H-Y (ref. 1), but the molecular nature of H-Y antigen has r emained obscure. Hya, the murine locus controlling H-Y expression, has been localized to Delta Sxr(b), a deletion interval of the short arm of the Y chromosome(2). In mice, H-Y antigen comprises at least four d istinct epitopes, each recognized by a specific T lymphocyte clone. It has recently been shown that one of these epitopes, H-YKk, is a pepti de encoded by the Y-linked Smcy gene, presented at the cell surface wi th the H-2K(k) major histocompatibility complex (MHC) molecule(3). How ever, deletion mapping and the analysis of variable inactivation of H- Y epitopes has suggested that the Hya locus may be genetically complex (4,5). Here we describe a novel mouse Y chromosome gene which we call Uty (ubiquitously transcribed tetratricopeptide repeat gene on the Y c hromosome). We identify the peptide WMHHNMDLI derived from the UTY pro tein as an H-Y epitope, H-YDb. Our data formally demonstrate that H-Y antigen is the product of more than one gene on the Y chromosome.