Characterization of β 2-microglobulin coding sequence from three non-placental mammals: the duckbill platypus, the short-beaked echidna, and the grey short-tailed opossum

Abstract

To further characterize genes of immunological importance from non-placental mammals, cDNAs encoding β 2-microglobulin (β 2m) were isolated from two prototherians, the platypus and an echidna, and one metatherian, a grey short-tailed opossum. In addition, a second allele of β 2m 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 β 2m was constructed that supports the classic view of evolution with prototherians as the basal mammalian group.