Comparative and Evolutionary Aspects of δ‐Crystallin in the Vertebrate Lens

We have utilized [ 3 H]cDNA · DNA annealing (using S 1 endonuclease resistance as an assay) to detect the presence of sequences complementary to chick δ‐crystallin mRNA in the genome of fish (salmon, herring), amphibians (frog, newt), reptiles (python, gekko, caiman), birds (quail, turkey, duck), and mammals (mouse, calf), and have compared several physical parameters of δ‐crystallin of the reptiles and birds. The rate and extent of chick δ‐crystallin [ 3 H]cDNA · DNA annealing were comparable among the birds, and indicated that the δ‐crystallin sequences are in the unique fraction of the genome. On the average, about one‐fifth as much annealing took place with the reptiles as with the birds, and no annealing was observed with the fish, amphibians and mammals. The avian and reptilian δ‐crystallins had subunit molecular weights near 50000 and native molecular weights near 2, as judged by sodium dodecylsulfate/urea/polyacrylamide gel electrophoresis and agarose gel chromatography, respectively, indicating that the subunit structure of δ‐crystallin has been largely conserved. Electrophoresis of the peptides generated by digestion with Staphylococcus uureus V8 protease indicated that the primary structures of the different reptilian and avian δ‐crystallins were similar but not identical. The isoelectric points of the δ‐crystallins ranged between pH 5 and 7, depending on the organism. In general, the reptilian δ‐crystallins had the higher isoelectric points.