Two structurally closely related polypeptides encoded by 14-S mRNA isolated from rat lens

14-S mRNA from rat lens codes for two subunits of alpha-crystallin, A2 (Mr 20 000) and AIns (Mr 24 000, previously referred to as alphaX). Structural relationship between both translation products has been proved by immunoprecipitation with antisera directed against the different crystallin classes. Competition immunoprecipitation showed that the 14-S mRNA translation products are precipitated by common antibodies, specific for the A subunit of alpha-crystallin. Two-dimensional gel electrophoresis and peptide analysis provided further evidence that the 24 000-Mr polypeptide, synthesized in vitro under direction of 14-S mRNA, is identical with native alphaAIns. Although the structures of alphaA2 and alphaAIns are very similar, no precursor-product relationship exists between both 14-S-mRNA-encoded polypeptides.