Human lens gamma-crystallins: isolation, identification, and characterization of the expressed gene products.

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Abstract
We have isolated the individual .gamma.-crystallins expressed in young human lenses and identified with which of the six known human .gamma.-crystallin genes they each correspond. We find that at least 90% of the .gamma.-crystallins synthesized in the young human lens are the products of genes .gamma.G3 and .gamma.G4. We demonstrate that .gamma.G4-crystallin undergoes a temperature-dependent phase separation, and we have measured the low-concentration branch of its coexistence curve (phase separation temperature vs. concentration) up to about 40 mg/ml. By comparison, we found no evidence of .gamma.G3-crystallin phase separating, even at lower temperatures and higher concentrations. This is consistent with predictions based on sequence homology between human and rat .gamma.-crystallins. The implications of these findings for human inherited and senile cataracts are considered.