Allelic variation in the mouse Tap-1 and Tap-2 transporter genes.

The TAP1 and TAP2 proteins form a heterodimer that transports short peptides from the cytosol into the endoplasmic reticulum lumen. Extensive allelic polymorphism of the rat TAP transporter has been shown to affect the repertoire of peptides presented by MHC class I molecules. Structural polymorphism in the human TAP genes is much more limited and has not been observed to have functional consequences. We have examined the polymorphism in mouse TAP1 and TAP2 in inbred mice. While the number of polymorphic positions in these molecules is more similar to that in human than to that in the rat, all strains examined have a structurally unique TAP transporter, suggesting the possibility of functional polymorphism. Furthermore, allelic variations in the mouse transporter are predominantly located in or adjacent to membrane-spanning domains, although no significant bias in the ratio of nonsynonymous to synonymous substitutions is observed. We also report that mouse TAP1 begins 172 amino acids upstream of the previously published start site and report the genomic organization of mouse Tap-1 and Tap-2.