Compound microsatellites in complete Escherichia coli genomes.

Compound microsatellites consisting of two or more repeats in close proximity have been found in eukaryotic genomes. So far such compound microsatellites have not been investigated in any prokaryotic genomes. We have therefore examined compound microsatellites in 22 complete genomes of Escherichia coli, which is one of the ideal model organisms to analyze the nature and evolution of prokaryotic compound microsatellites. Our results indicated that about 1.75-2.85% of all microsatellites could be accounted as compound microsatellites with very low complexity, and most compound microsatellites were composed of very different motifs. Compound microsatellites were significantly overrepresented in all surveyed genomes. These results were dramatically different from those in eukaryotes. We discussed the possible reasons for the observed divergence.