Organization of long repeats of sex-chromosomal heterochromatin in common vole species

Two long repeats, MS3 and MS4, are predominantly located in sex-chromosomal heterochromatin in common vole species [1]. Their tandem arrangement was r evealed by means of the PCR analysis of genomic DNAs of four Microtus speci es and by restriction mapping of clones selected from a M. rossiaemeridiona lis genomic library. Several mobile elements proved to be incorporated in a monomeric unit of each repeat and amplified together with its other compon ents. In addition, LINE inserts were found in MS4 tandem arrays. The copy n umber of both repeats per haploid genome was estimated at 100-300 for euchr omatin and 20,000-40,000 for the M. rossiaemeridionalis genome. The repeats were assumed to be the major component of sex-chromosomal heterochromatin DNA.