Comparison of the crystallin mRNA populations from rat, calf and duck lens. Evidence for a longer alpha A2-mRNA and two distinct alpha B2-mRNAs in the birds.

Total cytoplasmic poly(A)-containing RNA from rat, calf and duck lens was fractionated by electrophoresis in methylmercury hydroxide-containing agarose gels. RNA electrophoresed in parallel lanes was either transferred onto nitrocellulose and hybridized with total cDNA synthesized on the initial mRNA or was recovered from individual gel fractions for in vitro translation in a reticulocyte cell-free system. This allowed the identification and size-characterization of individual mRNA species encoding alpha-, beta-, gamma- and delta-crystallin polypeptides. The 14 S mRNA fraction of rat lens comprises two alpha A2-mRNAs of approximately 1250 and 1350 nucleotides and the alpha AIns-mRNA with a size similar to that of the largest alpha A2-mRNA. The calf lens 14 S mRNA fraction harbors a heterogeneous population of alpha A2-mRNA. In the same fraction another mRNA encoding a polypeptide, designated X, has been found sharing no homology with alpha A sequences. The duck lens alpha A2-mRNA appears to be 400-450 bases longer than the rat and calf lens alpha A2-mRNAs. Furthermore, in contrast to the single alpha B2-mRNA in rat and calf lens, two alpha B2-mRNAs have been identified in duck lens, one, the major species, similar in size to the alpha B2-mRNA in rat and calf lens (800 bases), and the other species 700 nucleotides longer. The large size differences among the alpha A2- and alpha B2-mRNAs most likely reside in their 3'-untranslated sequences.