The absence of the long 3'-non-translated region in mRNA coding for eye lens αA2-crystallin of the frog (Rana temporaria)

AbstractThe nucleotide sequence of a cloned cDNA (clone pRt(1)297; GENE (1982) 17, 131) coding for a 18 kDa polypeptide of the frog eye lens has been determined. The sequence, 791 nucleotide in length has only one long open reading frame (447 nucleotides). The derived amino acid sequence in this frame has > 90% homology with the region 25–173 of αA2-crystallin amino acid sequence from a related frog species Rana pipiens. The 5'-terminal part of mRNA corresponding to the first 24 amino acids of αA2-crystallin has been lost in cloning and substituted by an artefactual sequence. The 3'-terminal part appears to be intact as follows from the presence of the universal poly(A) addition site and poly(A) tract. The 3'-nontranslated region present in frog αA2-crystallin mRNA (130 nucleotides) is about 4-times shorter than in mammalian αA2-crystallin mRNA. Intact αA2-crystallin mRNA with a size of about 700 nucleotides as determined by Northern blot hybridization is about twice smaller than corresponding mammalian mRNAs

A novel type of crystallin in the frog eye lens 35-kDa polypeptide is not homologous to any of the major classes of lens crystallins

AbstractThe nucleotide sequence of a cloned DNA coding for the 35-kDa polypeptide of the eye lens of the frog Rana temporaria has been determined. The sequence without connectors and poly(A) tract is 889 nucleotides in length and shows no homology with sequences coding for other classes of crystallins; α-, β-, γ- or δ-crystallins. The sequence contains one reading frame 675 nucleotides in length, an apparently intact 3′-non-translated region with the polyadenylation signal sequence and a poly(A) tract; the 5′-non- translated region is lost along with part of the coding region; this accounts for about 1/4 of the total mRNA length. The secondary structure prediction according to the Ptitsin-Finkelstein method shows the presence of predominantly β-strands with only a few α-helical regions. We conclude that the 35-kDa polypeptide from the frog eye lens belongs to a new class of eye lens crystallins for which we propose the name ϵ-crystallin