Drybench Plasmid.
Promoters on a plasmid map
A promoter is where RNA polymerase binds to start a transcript; on a map it is drawn just upstream of the gene it drives.
Bacterial promoters
Bacterial RNA polymerase recognises short sequences upstream of the start of transcription; one of them, about ten bases upstream, was found in phage T7's early promoters (Pribnow 1975).
The lac promoter is controlled by the lac repressor, which binds the lac operator beside it (Gilbert and Maxam 1973) and blocks transcription until an inducer such as IPTG releases it. pUC19's map shows the lac promoter, the operator and the CAP binding site, each matched exactly by the library.
Phage promoters for expression
The T7 promoter is read only by T7 RNA polymerase, which is very active and specific, so a gene behind it is expressed strongly in a host that supplies the polymerase and hardly at all otherwise (Studier and Moffatt 1986). Many vectors place T7 and SP6 promoters on either side of a cloning site so that RNA can be made from either strand.
See it on a real plasmid
Open pUC19 and find the lac promoter, the lac operator and the CAP binding site beside the cloning site.
A promoter is where transcription starts; the tour shows RNA polymerase II copying a gene in a human cell.
References
- Pribnow D. Nucleotide sequence of an RNA polymerase binding site at an early T7 promoter. Proc Natl Acad Sci U S A 1975;72:784-788. PubMed 1093168
- Gilbert W, Maxam A. The nucleotide sequence of the lac operator. Proc Natl Acad Sci U S A 1973;70:3581-3584. PubMed 4587255
- Studier FW, Moffatt BA. Use of bacteriophage T7 RNA polymerase to direct selective high-level expression of cloned genes. J Mol Biol 1986;189:113-130. PubMed 3537305
Statements summarised by the site's builder from the references, for scientific review.