Gopaul, Krishna Kumar; (2003) Transcription of the Mycobacterium tuberculosis recA gene. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The human pathogen Mycobacterium tuberculosis is an intracellular parasite that infects macrophages. Within these cells, the pathogen is subjected to a number of DNA damaging compounds produced as part of the host's defence mechanism. Furthermore, M. tuberculosis can remain in a latent but viable phase for a long period of time after primary infection and within this time DNA damage might be expected to occur. Damage to DNA affects viability and therefore it is necessary for the pathogen to possess adequate DNA repair mechanisms. The RecA protein is central to many processes of DNA repair, having a regulatory role in the expression of other DNA repair genes as well as a direct role in recombinational repair. Therefore, it is of interest to study how control of M. tuberculosis recA transcription is facilitated. Primer extension and transcriptional fusions to a reporter gene have previously shown that the region upstream of the M. tuberculosis recA gene possesses two promoters. Putative promoter motifs were identified based on known E. coli promoter sequences. Through direct and random base changes the promoter elements were defined. In addition, studies of both promoters in DNA damage free and induced states highlighted differences in the activity of the elements. Another approach to study the regulation of recA transcription was to disrupt the activity of sigma factors within the pathogen. To this end, two novel sigma factor mutants, ΔsigC and ΔsigD were created. These mutant strains were transformed with constructs carrying the two promoters and induced with a DNA damaging agent to see if there was any change in the activity of either promoter which in turn could link the sigma factor to that DNA element. In addition, the effect of the ΔsigC mutation on the expression of other M. tuberculosis genes was assessed by microarray analysis.

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