Nucleotide sequences flanking dinucleotide microsatellites in the human, mouse and drosophila genomes

We extracted nucleotide sequences from the EMBL database that flank dinucle otide microsatellites in the long sequenced parts of the human, mouse and d rosophila genomes. Comparison of the flanking sequences showed that the mic rosatellites were mostly connected to the bulk of genomic DNA through conse rved, highly non-random and mostly (A+T)-rich sequences having many dozens of nucleotides in length. In many cases, the connectors were mutated versio ns of the flanked microsatellites whose sequence pattern gradually vanished with the distance from the microsatellite center. Hence many microsatellit es have hundreds rather than dozens of nucleotides in length, and their end s are diffuse. In contrast, some microsatellites containing predominantly C and/or G, did not influence their neighborhood at all. These results make us change notions about the microsatellite nature. They also indicate that the microsatellites are the dominant part of eukaryotic genomes.