IDENTIFICATION AND ANALYSIS OF EXTENDED -10 PROMOTERS FROM MYCOBACTERIA

Earlier studies from our laboratory on randomly isolated transcription al signals of mycobacteria had revealed that the -10 region of mycobac terial promoters and the corresponding binding domain in the major sig ma factor are highly similar to their Escherichia coli counterparts. I n contrast, the sequences in -35 regions of mycobacterial promoters an d the corresponding binding domain in the major sigma factor are vastl y different from their E. coli counterparts (M. D. Bashyam, D. Kaushal , S. K. Dasgupta, and A. E. Tyagi, J. Bacteriol. 178:4847-1853, 1996). We have now analyzed the role of the TGN motif present immediately up stream of the -10 region of mycobacterial promoters. Sequence analysis and site-specific mutagenesis of a Mycobacterium tuberculosis promote r and a Mycobacterium smegmatis promoter reveal that the TGN motif is an important determinant of transcriptional strength in mycobacteria, We show that mutation in the TGN motif can drastically reduce the tran scriptional strength of a mycobacterial promoter. The influence of the TGN motif on transcriptional strength is also modulated by the sequen ces in the -35 region. Comparative assessment of these extended -10 pr omoters in mycobacteria and E. coli suggests that functioning of the T GN motif in promoters of these two species is similar.