Sketching out regulatory bacterial gene transcription molecular mechanisms. (1) The RNA polymerase must bind to a transcription factor called sigma factor, to be able to transcribe DNA to RNA. (2.a) The sigma factor specifically recognizes a transcription promoter DNA sequence motif, upstream part of the gene, and drives the RNA polymerase to it. (2.b) DNA is copied into RNA from the Transcriptional Start Site (TSS), while the sigma factor is released and available for another RNA polymerase. (3.a) A transcriptional regulator binds to a specific motif around the promoter site, and in this example (3.b) activates transcription.