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The mechanism of upstream activation in the rrnB operon of Mycobacterium smegmatis is different from the Escherichia coli paradigm

K. G. Papavinasasundaram^1,

M. Joseph Colston^1,

¹ Division of Mycobacterial Research, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK
² Division of Protein Structure, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK

Correspondence
Kristine B. Arnvig
karnvig{at}nimr.mrc.ac.uk

Mycobacteria are slow-growing bacteria with a generation time of from 2–3 h up to several weeks. Consistent with the low growth rate, mycobacterial species have a maximum of two rRNA operons, rrnA and rrnB. The rrnA operon is present in all mycobacteria and has between two and five promoters, depending on species, whereas the rrnB operon, with a single promoter, is only found in some of the faster-growing species. The promoter region of the rrnB operon of a typical fast grower, Mycobacterium smegmatis, was investigated. By using lacZ reporter gene fusions it was demonstrated that the rrnB operon contains a highly activating region upstream of the core promoter, comparable to other bacterial rrn operons. However, the results suggest that, unlike the situation in, for example, Escherichia coli, the activating mechanism is solely factor dependent, and that no UP element is involved.

*Present address: Indian Institute of Science, Bangalore 560012, India.

Present address: Department of Medicine, Division of Infectious Diseases, University of British Columbia, Vancouver, Canada V5Z 3J5.

Deceased 20 February 2003.

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