A feline class II alpha gene with striking similarity to the HLA-DPA pseudogene

A genomic library was constructed from DNA of a domestic cat and screened with a human HLA-DR alpha probe at low stringency. Several positive clones were isolated, and the DNA sequence of one of these clones was determined. Comparison with class II alpha gene sequences from other species suggested that the feline gene is a DPA homologue (FLA-DPA) showing 84% similarity with HLA-DP alpha 1 in the exon encoding the second domain. The FLA-DPA gene that was isolated is a pseudogene, as two frame-shift mutations are present: one in the exon encoding the second domain, causing premature termination of translation, and one in the exon encoding the transmembrane region. The latter mutation and the further deletion of two codons in the transmembrane exon show a remarkable resemblance to the same exon of the human pseudogene, HLA-DPA2. Hence, both pseudogenes evolved from the same ancestral gene. The inactivation of this DPA gene could therefore have occurred prior to the major mammalian divergence.