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Journal of Bacteriology, November 1998, p. 5756-5761, Vol. 180, No. 21
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Roles of Multiple Promoters in Transcription of Ribosomal DNA: Effects of Growth Conditions on Precursor rRNA Synthesis in Mycobacteria

J. A. Gonzalez-y-Merchand,dagger M. J. Colston, and R. A. Cox*

Division of Mycobacterial Research, National Institute for Medical Research, London NW7 1AA, United Kingdom

Received 23 April 1998/Accepted 24 August 1998

The roles of multiple promoters in the synthesis of rRNA under different conditions of growth were investigated, using two mycobacterial species as model organisms. When Mycobacterium smegmatis was grown under optimal conditions, its two rRNA operons contributed equally, with two promoters, one from each operon, being responsible for most transcripts. In stationary-phase growth or balanced growth under carbon starvation conditions, one operon (rrnAf) dominated and its three promoters contributed more equally to the generation of transcripts. Mycobacterium tuberculosis has a single operon with two promoters, one of which generated 80% of transcripts, at all stages of growth. We infer that each promoter functions independently according to its intrinsic strength when cells are growing slowly so that one operon with three promoters is roughly equivalent to three operons with one promoter; at high growth rates, occlusion effects reduce the efficiency of multiple promoters to that of a single promoter.

* Corresponding author. Mailing address: Division of Mycobacterial Research, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom. Phone: 44 181 959 3666. Fax: 44 181 906 4477. E-mail: rcox{at}nimr.mrc.ac.uk.

dagger Permanent address: Departamento de Microbiologia, Escuela Nacional de Ciencias Biologicas, IPN, Mexico, D.F. 06400, Mexico.

Journal of Bacteriology, November 1998, p. 5756-5761, Vol. 180, No. 21
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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