The alpha-gliadin gene family .2. DNA and protein sequence variation, subfamily structure, and origins of pseudogenes

The derived amino-acid sequences of all reported alpha-gliadin clones are compared and analyzed, and the patterns of sequence change within the alpha-gliadin family are examined. The most variable sequences are two polyglutamine domains. These two domains are characteristic features of the alpha-gliadin storage proteins and account for most of the variation in protein size of this otherwise highly conserved protein family. In addition, their encoding DNA sequences form microsatellites. Single-base substitutions in the alpha-gliadin genes show a preponderance of transitions, including the C to T substitution which contributes to the generation of stop codons, and consequently to the observation that approximately 50% of the alpha-gliadin genes are pseudogenes. In one unusual gene, a microsatellite has expanded to 321 bp as compared to the normal 36-72 bp, and may result from similar mechanisms that produce polyglutamine-associated genetic diseases in humans. A comparison of the 27 reported sequences show several alpha-gliadin gene subfamilies, at least some of which are genome specific.