SEQUENCE-ANALYSIS OF HLA-BW53, A COMMON WEST AFRICAN ALLELE, SUGGESTS AN ORIGIN BY GENE CONVERSION OF HLA-B35

In the West African population of the Gambia the class I antigen HLA-Bw53 is found at high frequency. We used the polymerase chain reaction to amplify cDNA from an individual homozygous for this allele and determined the nucleotide sequence of the polymorphic-alpha-1 and alpha-2 domains. The HLA-Bw53 sequence is identical to HLA-B35 except for a short sequence at the 3' end of exon 2 (encoding the alpha-1 domain) which specifies a Bw4 rather than a Bw6 motif. This suggests an origin for HLA-Bw53 involving a gene conversion of HLA-B35 by an allele containing this Bw4 sequence. The alpha-2 domain shared by HLA-Bw53, -B35, and -Bw58 is particularly common in sub-Saharan Africans.