Repetitive DNA sequences in the common vole: cloning, characterization andchromosome localization of two novel complex repeats MS3 and MS4 from the genome of the East European vole Microtus rossiaemeridionalis

We have characterized two novel, complex, heterochromatic repeat sequences, MS3 and MS4, isolated from Microtus rossiaemeridionalis genomic DNA. Seque nce analysis indicates that both repeats consist of unique sequences interr upted by repeat elements of different origin and can be classified as long complex repeat units (LCRUs). A unique feature of both repeat units is the presence of short interspersed repeat elements (SINEs), which are usually c haracteristic of the euchromatic part of the genome. Comparative analysis r evealed no significant stretches of homology in the nucleotide sequences be tween the two repeats, suggesting that the repeats originated independently during the course of vole genome evolution. Fluorescence in situ hybridiza tion analysis demonstrates that MS3 and MS4 occupy distinct domains in the heterochromatic regions of the sex chromosomes in M. transcaspicus and M. a rvalis but collocalize in M. rossiaemeridionalis and M. kirgisorum heteroch romatic blocks. The localization pattern of the repeats on the vole chromos omes confirms the independent origin of the two repeats and suggests that e xpansion of the heterochromatic blocks has occurred subsequent to speciatio n.