ORGANIZATION OF THE ORIGINS OF REPLICATION OF THE CHROMOSOMES OF MYCOBACTERIUM-SMEGMATIS, MYCOBACTERIUM-LEPRAE AND MYCOBACTERIUM-TUBERCULOSIS AND ISOLATION OF A FUNCTIONAL ORIGIN FROM MYCOBACTERIUM-SMEGMATIS

The genus Mycobacterium is composed of species with widely differing g rowth rates ranging from approximately three hours in Mycobacterium sm egmatis to two weeks in Mycobacterium leprae, As DNA replication is co upled to cell duplication, it may be regulated by common mechanisms, T he chromosomal regions surrounding the origins of DNA replication from M. smegmatis, M. tuberculosis, and M. leprae have been sequenced, and show very few differences. The gene order, rnpA-rpmH-dnaA-dnaN-recF-o rf-gyrS-gyrA, is the same as in other Gram-positive organisms, Althoug h the general organization in M. smegmatis is very similar to that of Streptomyces spp,, a closely related genus, M, tuberculosis and M. lep rae differ as they lack an open reading frame, between dnaN and recF, which is similar to the gnd gene of Escherichia coil. Within the three mycobacterial species, there is extensive sequence conservation in th e intergenic regions flanking dnaA, but more variation from the consen sus DnaA box sequence was seen than in other bacteria, By means of sub cloning experiments, the putative chromosomal origin of replication of M. smegmatis, containing the dnaA-dnaN region, was shown to promote a utonomous replication in M. smegmatis, unlike the corresponding region s from M. tuberculosis or M. leprae.