Transporter associated with antigen-processing-1 (TAP1) alleles in Gorilla gorilla: diversification of the locus...

The transporter associated with antigen-processing (TAP) proteins are required for the transport of cytosolic peptides into the endoplasmic reticulum for assembly with class I major histocompatibility molecules. In the rat, allelic variants of the TAP genes impart specificity to the process of peptide transport. However, differential transport has yet to be demonstrated with the human molecules. TAP genes from humans and rodents have been studied thus far; analysis of another species more closely related to humans is necessary for a clearer understanding of the evolution of TAP genes. Three TAP1 alleles from four gorilla cell lines were characterized in this study. There is limited genetic distance at the locus, either within the gorilla (0.2%) or between the two hominoid species (0.8%). Nucleotide substitution analysis demonstrates that TAP1 and TAP2 are evolving at comparable rates under similar selection pressures. This pattern is in marked contrast to that observed for MHC class I genes of hominoids or rodents. Although there is limited evidence for trans-species evolution of the gorilla locus, the bulk of the diversification occurred after speciation as evidenced by a lack of shared amino acid polymorphism with human homologues. An evolutionary scheme predicts that the ancestral hominoid TAP1 molecule most closely resembled the human TAP1*02011.