Evolution of simple sequence in proteins.

The proteins of Saccharomyces cerevisiae contain a high proportion of low-complexity, simple sequences. These are protein segments composed almost exclusively or largely of a single repetitive amino acid polymer and are the most commonly shared feature between proteins. We have examined a survey of other species to determine how widespread this phenomenon might be. This was done by comparing how frequently segments from one protein are present in other proteins. Any recently evolutionarily related proteins were excluded. It was found that the most commonly shared features of eukaryotic proteins were repetitive but that prokaryotes did not contain such shared, extensively redundant repeats. The proportion of eukaryotic proteins that contain a significantly repetitive fraction changes dramatically from species to species. In addition the individual amino acids present in these repeats change between species. This suggests that the primary sequence of the repeats may not be important for their function. Further tests of the yeast repeats confirmed that these repeats evolve more quickly than the remainder of the protein sequence within which they are embedded. These results show that these rapid evolving, simple sequence repeats are in fact the most commonly shared pattern between all of the genomic proteins of eukaryotes.