Characterization of beta2-microglobulin coding sequence from three non-placental mammals: the duckbill platypus, the short-beaked echidna, and the grey short-tailed opossum

Miska, K. B., Hellman, L., and Miller, R. D.

Abstract:
To further characterize genes of immunological importance from non-placental mammals, cDNAs encoding beta2-microglobulin were isolated from two prototherians, the platypus and an echidna, and one metatherian, a grey short-tailed opossum. In addition a second allele of beta2-microglobulin was identified in another metatherian species, the brushtail possum. Analysis of the deduced translations revealed conservation of key residues in these molecules over a long evolutionary history. The types of nucleotide substitutions present among the various taxa are also consistent with purifying selection at this conserved locus. An evolutionary tree of beta2-microglobulin was constructed that supports the classic view of evolution with prototherians as the basal mammalian group.