Genomic organization of the X-linked inhibitor of apoptosis and identification of a novel testis-specific transcript.

Here we report the genomic organization and mapping of the X-linked inhibitor of apoptosis gene (BIRC4, also known as XIAP and hILP) and the identification of a closely related transcript. BIRC4 is located on Xq25 and is composed of seven exons. The intron/exon structure is highly conserved between the mouse homologue and its human counterpart. Four bands cross-react with a BIRC4 coding region probe on a genomic Southern blot. One of these cross-reactive bands encodes an intronless gene that expresses a 2.2-kb transcript solely in the testis. This testis-specific transcript contains a putative open reading frame (ORF) that is homologous to the carboxy-terminal end of BIRC4; overexpression of this ORF shows protective effects against BAX-induced apoptosis.