promoter

A region of DNA to which RNA polymerase binds before initiating the transcription of DNA into RNA. The nucleotide at which transcription starts is designated +1 and nucleotides are numbered from this with negative numbers indicating upstream nucleotides and positive downstream nucleotides. Most bacterial promoters contain two consensus sequences that seem to be essential for the binding of the polymerase. The first, the Pribnow box, is at about -10 and has the consensus sequence 5\'-TATAAT-3\'. The second, the -35 sequence, is centred about -35 and has the consensus sequence 5\'-TTGACA-3\'. Most factors that regulate gene transcription do so by binding at or near the promoter and affecting the initiation of transcription. Much less is known about eukaryote promoters; each of the three RNA polymerases has a different promoter. RNA polymerase I recognizes a single promoter for the precursor of rRNA. RNA polymerase II, that transcribes all genes coding for polypeptides, recognizes many thousands of promoters. Most have the Goldberg-Hogness or TATA box that is centred around position -25 and has the consensus sequence 5\'-TATAAAA-3\'. Several promoters have a CAAT box around -90 with the consensus sequence 5\'-GGCCAATCT-3\'. There is increasing evidence that all promoters for genes for "housekeeping" proteins contain multiple copies of a GC-rich element that includes the sequence 5\'-GGGCGG-3\'. Transcription by polymerase II is also affected by more distant elements known as enhancers. RNA polymerase III synthesizes 5s ribosomal RNA, all tRNAs, and a number of small RNAs. The promoter for RNA polymerase III is located within the gene either as a single sequence, as in the 5s RNA gene, or as two blocks, as in all tRNA genes.