BETA(2)-MICROGLOBULIN IN NEOTROPICAL PRIMATES (PLATYRRHINI)

Nucleotide sequences for the three exons of the beta(2)-microglobulin (beta(2)m) gene (B2m) were determined for 135 animals representing 37 species and all 16 genera of neotropical primates (Platyrrhini). Twent y-eight different nucleotide sequences, encoding for 26 different prot eins, were obtained. In comparison with those of other primate species , the beta(2)-microglobulins of the Platyrrhini form a distinct clade. Individual genera of neotropical primates have distinctive B2m sequen ces, but within a genera species can have either the same or different B2m sequences. B2m polymorphism was found within three of the species sampled: Callicebus personatus, Saguinus midas, and Aotus azarae. Of these only the polymorphism in A. azarae has an effect upon the mature , functional beta(2)m protein: residue 4 being either alanine or threo nine. The A. azarae B2m allele encoding alanine at position 4 is share d with another species of Aotus (A. infulatus). In pairwise com pariso n the mature beta(2)m proteins of neotropical primates differ by 1-9 a mino acid substitutions which can occur at 18 positions within the seq uence. The substitutions are distributed throughout the primary struct ure but are more commonly found in loops rather than beta strands of t he tertiary structure. Of 17 residues of beta(2)m which hydrogen-bond with the class I heavy chain in human MHC class I molecules, 13 are co nserved in the neotropical primates. The overall pattern of sequence v ariation in the B2m genes of the Platyrrhini is consistent with an evo lution by successive selectively neutral events.