Characterization of gamma-crystallins from a hybrid teleostean fish: multiplicity of isoforms as revealed by cDNA sequence analysis.

gamma-Crystallins were isolated and characterized from the eye lenses of a hybrid species belonging to the teleostean fish. Isoelectric focusing of gamma-crystallin fraction obtained from gel-permeation chromatography revealed that it consists of multiple charge isomers of a protein species with a molecular mass of about 20 kDa. To facilitate the cloning of gamma-crystallin gene, cDNA was constructed from the poly(A)+mRNA isolated from fresh lenses, and amplification by polymerase chain reaction (PCR) was carried out to obtain cDNA encoding multiple gamma-crystallins. Sequencing five of more than 10 positive clones revealed that a multiplicity of isoforms exists in the gamma-crystallin class of teleostean lenses. Comparison of protein sequences encoded by these multiple cDNAs with those published sequences of gamma-crystallins from bovine, mouse an carp lenses indicated that there is about 70-80% sequence homology between different species of piscine species whereas only 50-60% is found between mammals and fishes. Structural analysis of these gamma-crystallins with high methionine contents (11-16%) suggests that there are two major subclasses of piscine gamma-crystallins, i.e. gamma M 1 and gamma M 2, existed long before the appearance of mammalian gamma-crystallin with low methionines.