IDENTIFICATION OF NEW TAP2 ALLELES IN GORILLA - EVOLUTION OF THE LOCUS WITHIN HOMINOIDS

Transporters associated with antigen processing molecules (TAP1 and TA P2) mediate the transfer of cytosolic peptides into the lumen of the e ndoplasmic reticulum for association with newly synthesized class I mo lecules of the major histocompatibility complex. Previous molecular an d functional analyses of rat and human TAP2 homologues indicated major differences in gene diversification patterns and selectivity of pepti des transported. Therefore, in this study, we analyzed the alleles of the gorilla TAP2 locus to determine whether the pattern of diversifica tion resembled that in either of those two species. Sequence analysis of the TAP2 cDNAs from gorilla Epstein-Barr virus-transformed B-cell l ines revealed four alleles with a genetic distance of less than 1%. Th e nucleotide substitutions distinguishing the alleles are confined to the 3' half of the coding region and occur individually or within two small clusters of variability. Diversification of the locus appears to have resulted from point substitutions and recombinational events. Ev olutionary-rate estimates for the TAP2 gene in gorilla and human close ly approximate those observed for other hominoid genes. The amino acid polymorphisms within the gorilla molecules are distinct from those in the human homologues. The absence of ancestral polymorphisms suggests that gorilla and human TAP2 genes have not evolved in a trans-species fashion but rather have diversified since the divergence of the linea ges.