Codon reiteration and the evolution of proteins.

Sequence data banks have been searched for proteins possessing uninterrupted reiterations of any amino acid. Hydrophilic amino acids, and particularly glutamine, account for a large proportion of the longer reiterants. In the genes for these proteins, the most common reiterants are those that contain poly(CAG), even out-of-frame or, to a lesser degree, those that contain repeated doublets of CA, AG, or GC. The preferential generation of such reiterants requires that DNA strand-specific signals predispose to reiteration and thus to the extension of coding regions.