The eye lens crystallins: ambiguity as evolutionary strategy.

Comparative studies of the different families of lens-specific proteins of the vertebrates, the crystallins, and their genes reveal several interesting evolutionary features. The origin of alpha-crystallin can be traced back to the small heat shock proteins, while the superfamily of beta gamma-crystallins shows structural similarities with a bacterial spore coat protein. The crystallins display a great diversity within and between species, as well as during development. Ambiguous transcription, mRNA-processing, and translation contribute to this diversity of the crystallins and their expression. These mechanisms include the occurrence of atypical poly-A addition signals, alternative splicing, and the use of two initiation codons on a single mRNA.