The gene of the N-acetylglucosaminidase, a Bacillus subtilis 168 cell wall hydrolase not involved in vegetative cell autolysis

Authors

  • Philippe Margot,

    1. Institut de Génétique et Biologie Microbiennes, rue César-Roux, 19, 1005 Lausanne, Switzerland.
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    • Department of Molecular and Experimental Medicine, Division of Cellular Biology, The Scripps Research Institute, 10666 North Torrey Pines Road, La Jolla, California 92037, USA.

  • Catherine Mauël,

    1. Institut de Génétique et Biologie Microbiennes, rue César-Roux, 19, 1005 Lausanne, Switzerland.
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  • Dimitri Karamata

    Corresponding author
    1. Institut de Génétique et Biologie Microbiennes, rue César-Roux, 19, 1005 Lausanne, Switzerland.
    • *For correspondence. Tel. (21) 3206075; Fax (21) 3206078.

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Summary

lytD, the structural gene of the Bacillus subtilis 168 N-acetylglucosaminidase was localized at 310°, next to the tagABC operon. Sequence analysis revealed a monocistronic operon encoding a 95.6 kDa protein endowed with an export signal, the cleavage of which yields the monomer polypeptide (92.8 kDa) of the dimeric active form of the enzyme. Transcription is initiated at a sigma-D (σD)-dependent promoter and ends at a terminator common to lytD and the divergently transcribed tagABC operon. In addition, we report the sequence of the adjacent upstream ORF, transcribed in the same direction as lytD, which shows significant homology to phosphomannose isomerase-encoding genes. Cell separation, motility, autolysis, cell wall turnover and growth were not affected in strains devoid of the N-acetylglucosaminidase. A mutant deficient in the two most abundant autolysins, i.e. the LytC amidase and the glucosaminidase, exhibited the phenotype of the amidase-deficient strains, revealing their non-requirement for growth. This conclusion raises two fundamental questions: how does the cell undo the highly cross-linked peptidoglycan so as to be able to grow, and what is the rote of the considerable amount of autolysin normally present? Possible answers to these questions are discussed.

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