title: Sequence analysis of four acidic beta-crystallin subunits of amphibian lenses: phylogenetic comparison between beta- and gamma-crystallins.
abstract: beta-Crystallins composed of the most heterogeneous group of subunit chains among the three major crystallin families of vertebrates, i.e. alpha-, beta- and gamma-crystallins, are less well understood at the structural and functional levels than the other two. They comprise a multigene family with at least three basic (betaB1-3) and four acidic (betaA1-4) subunit polypeptides. In order to facilitate the determination of the primary sequences of all these ubiquitous crystallin subunits present in all vertebrate species, cDNA mixture was synthesized from the poly(A)+ mRNA isolated from bullfrog eye lenses. We report here a protocol of Rapid Amplification of cDNA Ends (RACE) was used to amplify cDNAs encoding beta-crystallin acidic subunit polypeptides by polymerase chain reaction (PCR). Four complete full-length reading frames with two each of 597 and 648 base pairs, which cover four deduced protein sequences of 198 (betaA1-1 and betaA1-2) and 215 (betaA3-1 and betaA3-2) amino acids including the universal initiating methionine, were revealed by nucleotide sequencing. They show about 96-98% sequence similarity among themselves and 76-80%, 80-83% to the homologous betaA1/A3 crystallins of bovine and human species respectively, revealing the close structural relationship among acidic subunits of all beta-crystallins even from remotely related species. In this study a phylogenetic comparison based on amino-acid sequences of various betaA1/A3 crystallins plus the major basic beta-crystallin (betaBp) and gamma-crystallin from different vertebrate species is made using a combination of distance matrix and approximate parsimony methods, which correctly groups these betaA crystallin chains together as one family distinct from basic beta-crystallins and gamma-crystallin and further corroborates the supposition that beta- and gamma-crystallins form a superfamily with a common ancestry.
authors.affiliation: Laboratory of Crystallin Research, Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan.
authors.forename: S F
authors.initials: SF
authors.lastname: Lu
authors.forename: F M
authors.initials: FM
authors.lastname: Pan
authors.forename: S H
authors.initials: SH
authors.lastname: Chiou
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003459:Crystallins / Q000235:genetics*; D018076:DNA, Complementary; D006801:Humans; D007908:Lens, Crystalline / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D011892:Rana catesbeiana; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D003459:Crystallins; D018076:DNA, Complementary