Characterization and taxonomic implications of the rRNA genes of Mycobacterium leprae

The number of rRNA genes of Mycobacterium leprae was determined by restriction analysis of M. leprae total chromosomal DNA. A single set of rRNA genes was found. This set was subcloned from a cosmid library of M. leprae DNA into pUC13 and was characterized by restriction analysis and hybridization with Escherichia coli rRNA genes. The 16S, 23S, and 5S genes of M. leprae were clustered on a 5.3-kilobase DNA fragment. On one hand, restriction analysis of the set of rRNA genes showed the uniqueness of M. leprae among mycobacteria, but on the other hand, it suggested that M. leprae strains of several origins are very much alike. Quantitative hybridization studies between M. leprae rDNA and total DNA of various bacteria demonstrated a close relatedness between M. leprae and corynebacteria, nocardia, and mycobacteria, especially Mycobacterium tuberculosis.