PRIMATE DRB6 GENE-EXPRESSION AND EVOLUTION - A STUDY IN MACACA-MULATTA AND CERCOPITHECUS-AETHIOPS

DRB6 has been found to be transcribed in human and apes. Promoter regi on and exon 1 come from a 5' LTR from a mammary tumour retrovirus. How ever, the putative protein structure would be very different to other DR molecules and it is doubtful that it may function as an antigen pre senting molecule. Primate DRB6 alleles previously published together w ith the two new macaque sequences reported here support the existence of a strong selective pressure working on exon 2 to generate stop codo ns at the end of the exon (between codons 74 and 94) during at least 2 3 million years. The topology of dendrograms constructed with differen t primate DRB6 alleles supports the ''trans-species'' evolution propos ed for MHC class I, class II and possibly C4 genes. Finally, DRB6, whi ch is one of the oldest DRB genes, has been lost in the HLA-DRB3 (or D R52) group of haplotypes (DR3, DR5, DR6 and DR8) and a small DRB6 sequ ence is present at the exon 2 first hypervariable region of DRB4 (or D R53) gene, which is present in DR4, DR7 and DR9 haplotypes.