Bacterial promoters are generally composed of two elements: one conserved sequence centered at –35 nucleotides and a second conserved sequence centered at –10 nucleotides from the start of the transcript, which is typically a purine nucleotide (A or G).
The terms –35 (TTGACA ) and –10 (Pribnow Box:TATAAT ) refer to the typical location of these sequences, although the number of base pairs separating them can vary among different promoters.
Transcription in bacteria is initiated by a
protein complex known as RNA polymerase (RNAP),
consisting of five subunits ( core enzyme) and an additional σ factor.
The σ factor is responsible for locating promoters by recognizing two binding sites, typically located at the -10 and -35 positions with respect to the transcription start site (TSS). Once transcription has begun, the σ factor dissociates and transcription continues with core enzyme alone.
Here two examples from two genes of M.ulcerans genome:
MUL 0007
MUL 0010
Practical rule
Pribnow Box: the first positons, TA,in general are preserved but the last T must be present in the promoter.
-35 region:TTG is highly preserved.
-43 region: there are some AT nucleotides.
