title: Sequence analysis of frog alpha B-crystallin cDNA: sequence homology and evolutionary comparison of alpha A, alpha B and heat shock proteins.
abstract: alpha-Crystallin is a major lens protein present in the lenses of all vertebrate species. Recent studies have revealed that bovine alpha-crystallins possess genuine chaperone activity similar to small heat-shock proteins. In order to facilitate the determination of the primary sequence of amphibian alpha B-crystallin, cDNA encoding alpha B subunit chain was amplified using a new "Rapid Amplification of cDNA Ends" (RACE) protocol of Polymerase Chain Reaction (PCR). PCR-amplified product corresponding to alpha B subunit was then subcloned into pUC18 vector and transformed into E. coli strain JM109. Plasmids purified from the positive clones were prepared for nucleotide sequencing by the automatic fluorescence-based dideoxynucleotide chain-termination method. Sequencing more than five clones containing DNA inserts coding for alpha B-crystallin subunit constructed only one complete full-length reading frame of 522 base pairs similar to that of alpha A subunit, covering a deduced protein sequence of 173 amino acids including the universal translation-initiating methionine. The frog alpha B crystallin shows 69, 66 and 56% whereas alpha A crystallin shows 83, 81 and 69% sequence similarity to the homologous chains of bovine, chicken and dogfish, respectively, revealing a more divergent structural relationship among these alpha B subunits as compared to alpha A subunits. Structural analysis and comparison of alpha A- and alpha B-crystallin subunits from eye lenses of different classes of vertebrates also shed some light on the evolutionary relatedness between alpha B/alpha A crystallins and the small heat-shock proteins.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D002417:Cattle; D003459:Crystallins / Q000737:chemistry / Q000235:genetics*; D018076:DNA, Complementary / Q000737:chemistry*; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics*; D006801:Humans; D007908:Lens, Crystalline / Q000737:chemistry; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D011892:Rana catesbeiana; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D003459:Crystallins; D018076:DNA, Complementary; D006360:Heat-Shock Proteins