How to recognize bacterial promoters

Identifying prokaryotic promoter sequences is difficult and for most sequenced bacterial genomes the promoter sequences are still unknown.
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.