Nonhuman primates represent phylogenetic intermediates for studying the divergence of human and murine β2Ms. We report the nucleotide sequences of B2m cDNA clones from a baboon cell line, 26CB-1 (Papio hamadryas); primates: Cercopithecoida), and a cotton-top tamarin cell line, 1605L (Saguinus oedipus; primates: Ceboidea). The baboon and tamarin B2m sequences indicate a very slow rate of B2m evolution in primates relative to that in murid rodents. Phenotypic evolution of β2M has also been very conservative in primates, with only 9-14 substitutions separating baboon or tamarin β2Ms from those of humans or orangutans. Analyses of silent and amino-acid-altering nucleotide substitutions provide evidence that negative selection has acted to limit variability in β strands of primate β2Ms, while positive selection has promoted diversity in non-β-strand regions of murine β2Ms. No evidence for the action of selection upon β2M residues that contact the class I heavy chain was found in primates or mice. The finding that different selective forces have operated upon primate and murine β2Ms suggests that β2M may have evolved to serve distinct functions in primates and mice.
|Number of pages||7|
|State||Published - Mar 1994|