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Is all lab bacterial strains have t7 RNA polymerase gene... - (Sep/05/2006 )


Hope you can help me out. Been searching the net with no concrete result.
Is all lab E. coli strains have a t7 RNA pol integrated into their chromosomes? E.g. DH5a, xl1-blue, JM109 etc...

Appreciate your reply.


-I love MSGs!-

No, T7 RNA polymerase is only present in the (DE3) lambda integration strains, such as BL21 (DE3).
This is useful for cloning toxic proteins in normal E. coli strains, where there is little or no expression.
See genotypes of common lab strains at:


Thanks, the link is helpful.

I've been looking at different vectors that have blue white screening capability (i.e. lacZ) and it's confusing to see that T7 promoter is normally highlighted with the lacZ whereas lac promoter (if present) is not mentioned. I was wondering if lacZ expression in these vectors is being driven by T7 promoter or lac promoter. Could you help me on this.


-I love MSGs!-

You are probably looking at the T7 sites on these vectors which are intended as primer binding sites for sequencing, rather than promoters for expression. The M13-F, M13-R, SP-6, T3, and T7 primers are all common primer sequences on many vectors. Sequencing companies often stock these primers, so that you don't need custom primers for each different vector. See:


Thanks smile.gif.

Ohya, apart from sequencing purpose, I guess t7 promoter can be used in vitro transcription/translation systems as well, or simply to generate ssRNAs. I know now that not all vectors with t7 promoter will express proteins in all e. coli host. Only when t7 and t7 rna polymerase are present, will the e. coli express the protein.


-I love MSGs!-