Transcription of rDNA in mycobacteria

Arnvig, Kristine Bourke (2001). Transcription of rDNA in mycobacteria. PhD thesis The Open University.



The genus Mycobacterium consists of numerous species, which display large variations in growth requirements and growth rates. They do however have certain common characteristics including growth rates that are lower than those of many other bacteria and a low number of rrn operons. As a rule the slower growing species, including the human pathogen Mycobacterium tuberculosis, have a single rrn operon, rrnA, and the faster growing species have two operons, rrnA and rrnB. The promoters of these opérons vary between species and they display differential regulation upon a change in growth conditions. Nothing is known about the regions responsible for the regulation of rrn expression. In the present study DNA fragments from the promoter and leader regions of mycobacterial rrn operons were fused to a promoter-less lacZ gene and the resulting reporter constructs were assayed for ß-galactosidase activity. This investigation led to the identification of a number of regulatory regions, which act at different stages of gene expression and with different effects. The results demonstrate that the two opérons have certain features in common. These include a highly activating upstream region and a downstream/leader region that suppresses rrn expression. In vitro interactions between the M.tb rrn leader and M.tb Nus factors furthermore suggest that the M.tb rrn anti-termination mechanism may differ significantly from the E. coli paradigm.

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