A pseudo-exon in the functional humanαA-crystallin gene

The frequent correspondence of exons to structural or functional domains in proteins has suggested that many proteins have evolved by modular assembly1. This idea is supported by examples of apparent exon duplication and by shared domains among both alternatively spliced and completely separate genes1–4. During this process it is probable that some combinations of exons would not prove advantageous and would therefore be lost. Here we report that within the active single-copy human gene for αA-crystallin there is a 'pseudo-exon' in the early stages of being extinguished, perhaps the result of a failed experiment in the evolution of this specialized, lens-specific protein.