Homology between the primary structures of the major bovine β‐crystallin chains

Abstract

Partial amino acid sequences of six major subunits of bovine β‐crystallin have been determined by automatic liquid‐phase Edman degradation and the dansyl‐Edman procedure, complemented by amino acid analyses of peptides. The results show that, including the previously established βBp sequence [H. P. C. Driessen et al. (1981) Eur. J. Biochem. 121, 83–91], there exist at least seven primary gene products in bovine β‐crystallin, which exhibit 40% or more sequence homology. Two of the gene products are completely identical except for the presence in one of them of 17 additional residues at the N terminus, possibly caused by differential splicing of the same primary RNA transcript. The rate of evolutionary change of the β chains (4% sequence change per 100 × 106 years) is about equally slow as that of α‐crystallin, and the gene duplications giving rise to the different chains must have occurred very early in vertebrate evolution. The β chains can be divided into two groups, according to sequence homology and presence of deletions/insertions and C‐terminal extension, on which basis a new, rational nomenclature for the β subunits is introduced. The N‐terminal extensions of all β chains are very different in length and sequence, even between homologous β chains in different species. Possible explanations for this finding are discussed. Copyright © 1984, Wiley Blackwell. All rights reserved