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

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