This review describes the complex structure and characteristics of mycobacterial promoters, in comparison to the classical E.?coli prokaryotic promoter structure. Some components of mycobacterial promoters are similar to those of E. coli. These include the predominant guanine residue at the transcriptional start point, conserved??10 hexamer, similar interhexameric distances, the use of ATG as a start codon, the guanine- and adenine-rich ribosome binding site and the presence of extended??10 (TGn) motifs in strong promoters. However, these components are much more variable in sequence in mycobacterial promoters and no conserved??35 hexamer sequence (clearly defined in E.?coli) can be identified. This may be a result of the high G + C content of mycobacterial genomes, as well as the large number of sigma factors present in mycobacteria, which may recognise different promoter sequences. Mycobacteria possess a complex transcriptional regulatory network. Numerous regulatory motifs have been identified in mycobacterial promoters, predominantly in the interhexameric region. These are bound by specific transcriptional regulators in response to environmental changes.
The combination of specific promoter sequences, transcriptional regulators and a variety of sigma factors enables rapid and specific responses to diverse conditions and different stages of infection. This review aims to provide an overview of the complex architecture of mycobacterial transcriptional regulation.