Primary Gene Products of Bovine β‐Crystallin and Reassociation Behavior of Its Aggregates

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Abstract
.beta.-Crystallin from calf lens cortex was fractionated in 3 different aggregates of increasing size: .beta.L2, .beta.L1 and .beta.H, of which the subunit composition was revealed by 2-dimensional gel electrophoresis. While .beta.L2 mainly consists of .beta. Bp (the major polypeptide chain in all 3 aggregates), .beta.L1 is characterized by the addition of a neutral and 2 acidic chains, and .beta.H contains 2 basic chains. Translation of calf lens polyribosomes in a reticulocyte cell-free system allowed the identification of 6 .beta.-crystallin subunits as primary gene products. The distribution of these newly synthesized polypeptides over the 3 aggregates was established after gel filtration in the presence of carrier lens proteins. The aggregation behavior of the .beta.-crystallin chain was studied by dissociation/reassociation experiments. The 3 separate aggregates could be reversibly dissociated. Reassociation of basic, neutral and acidic polypeptides, isolated by ion-exchange chromatography of .beta.-crystallin, produced a .beta.H-like aggregate. The neutral and acidic polypeptides reassociated into a .beta.L1-like aggregate, while the neutral polypeptides gave dimers like .beta.L2. A .beta.H-like aggregate could also be obtained by reaggregation of .beta.L2 with the acidic and basic chains of .beta.H. A preliminary model for the formation of .beta.-crystallin aggregates is discussed.