Characterization of a Minimal Type of Promoter Containing the −10 Element and a Guanine at the −14 or −13 Position in Mycobacteria

Three key promoter elements, i.e., −10, −35, and T−15 G−14 N, are recognized by the σ subunit of RNA polymerase. Among them, promoters with the −10 element and either −35 or T−15 G−14 N are known to initiate transcription efficiently, but recent systematic analyses have identified a large group of promoters inMycobacterium tuberculosis that contain only a −10 consensus. How these promoters initiate transcription remains poorly understood. Here, we show that promoters containing the −10 element and an upstream G located at the −14 or −13 position can successfully initiate transcription in mycobacteria. Importantly, this new type of promoter is active in the absence of other promoter consensuses, suggesting that it is a minimal promoter type. Mutation of the upstream G in promoters decreased the efficiencies of their binding with RNA polymerase and their abilities to initiate transcription in bothin vitro andin vivo analyses. A glutamic acid in σ region 3.0 is essential for recognizing G−14 and G−13 and is conserved in both principal and principal-like σ factors in mycobacteria, indicating that recognition of this minimal type of promoter might be a common mechanism for transcription initiation. Consistently, more than 70% of the identified promoters inM. tuberculosis contained G−14 or G−13 upstream of the conserved −10 element, and thousands of promoters in representative mycobacterial species have been predicted using the −10 consensus and G−14 or G−13 . Altogether, our study presents a universal mechanism for transcription initiation from a minimal promoter in mycobacteria, which might also be applicable to other bacteria.IMPORTANCE In contrast to the detailed information for recognizing classic promoters in the model organismEscherichia coli , very little is known about how transcription is initiated in the human pathogenMycobacterium tuberculosis . In this study, we characterized a new type of promoter in mycobacteria that requires only a −10 consensus and an upstream G−14 or G−13 . Residues important for recognizing the −10 element and the upstream G are conserved in σA and σB from mycobacterial species. According to such features, thousands of promoters in mycobacteria can be predicted using the −10 consensus and G−14 or G−13 , which suggests that transcription from this new type of promoter might be widespread. Our findings provide insightful information for characterizing promoters in mycobacteria.