Organization of the origins of replication of the chromosomes of Mycobacterium smegmatis, Mycobacterium leprae and Mycobacterium tuberculosis and isolation of a functional origin from M. smegmatis

Authors

  • Leirla Salazar,

    1. Laboratorio de Genética Molecular, Centro de Microbiología y Biología Celular, Instituto Venezolano de Investigaciones Científicas (IVIC),Caracas, 1020A Venezuela.
    2. Unité de Génétique Moléculaire Bactérienne, Institut Pasteur, 28 rue du Dr Roux, 75724 Paris Cedex 15, France.
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  • Hafida Fsihi,

    1. Unité de Génétique Moléculaire Bactérienne, Institut Pasteur, 28 rue du Dr Roux, 75724 Paris Cedex 15, France.
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  • Edda de Rossi,

    1. Unité de Génétique Moléculaire Bactérienne, Institut Pasteur, 28 rue du Dr Roux, 75724 Paris Cedex 15, France.
    2. Dipartimento di Genetica e Microbiologia, Universita di Pavia, 27100 Pavia, Italy.
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  • Giovanna Riccardi,

    1. Dipartimento di Genetica e Microbiologia, Universita di Pavia, 27100 Pavia, Italy.
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  • Carmen Rios,

    1. Laboratorio de Genética Molecular, Centro de Microbiología y Biología Celular, Instituto Venezolano de Investigaciones Científicas (IVIC),Caracas, 1020A Venezuela.
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  • Stewart T. Cole,

    1. Unité de Génétique Moléculaire Bactérienne, Institut Pasteur, 28 rue du Dr Roux, 75724 Paris Cedex 15, France.
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  • Howard E. Takiff

    Corresponding author
    1. Laboratorio de Genética Molecular, Centro de Microbiología y Biología Celular, Instituto Venezolano de Investigaciones Científicas (IVIC),Caracas, 1020A Venezuela.
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Summary

The genus Mycobacterium is composed of species with widely differing growth rates ranging from approximately three hours in Mycobacterium smegmatis to two weeks in Mycobacterium leprae. As DNA replication is coupled to cell duplication, it may be regulated by common mechanisms. The 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-orf-gyrB-gyrA, is the same as in other Gram-positive organisms. Although the general organization in M. smegmatis is very similar to that of Streptomyces spp., a closely related genus, M. tuberculosis and M. leprae differ as they lack an open reading frame, between dnaN and recF, which is similar to the gnd gene of Escherichia coli. Within the three mycobacterial species, there is extensive sequence conservation in the intergenic regions flanking dnaA, but more variation from the consensus DnaA box sequence was seen than in other bacteria. By means of subcloning experiments, the putative chromosomal origin of replication of M. smegmatis, containing the dnaA-dnaN region, was shown to promote autonomous replication in M. smegmatis, unlike the corresponding regions from M. tuberculosis or M. leprae.

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