Variable human minisatellite-like regions in the Mycobacterium tuberculosis genome

Mycobacterial interspersed repetitive units (MIRUs) are 40-100 bp DNA eleme nts often found as tandem repeats and dispersed in intergenic regions of th e Mycobacterium tuberculosis complex genomes. The M. tuberculosis H37Rv chr omosome contains 41 MIRU loci. After polymerase chain reaction (PCR) and se quence analyses of these loci in 31 M. tuberculosis complex strains, 12 of them were found to display variations in tandem repeat copy numbers and, in most cases, sequence variations between repeat units as well. These featur es are reminiscent of those of certain human variable minisatellites. Of th e 12 variable loci, only one was found to vary among genealogically distant BCG substrains, suggesting that these interspersed bacterial minisatellite -like structures evolve slowly in mycobacterial populations.