Modulation of tyrT promoter activity by template supercoiling in vivo.
AUTOR(ES)
Bowater, R P
RESUMO
We have found that initiation of RNA synthesis at the tyrT promoter of Escherichia coli can be stimulated on a plasmid by a factor of 4-6 by elevation of DNA supercoiling in vivo. Increased unconstrained plasmid supercoiling was achieved by inserting the tyrT promoter upstream of the tetracycline resistance gene tetA and transformation into a topA host. Under these conditions there is marked oversupercoiling of the plasmid DNA and we have shown previously that this can lead to increased promoter activity in the topological domain created. A critical element in the formation of this domain is the coupled transcription, translation and membrane insertion of tetA and we show that all of these events are important in the stimulation of tyrT promoter activity. The magnitude of the stimulation is in reasonable agreement with that measured in vitro as a function of plasmid supercoiling, if the unconstrained level of negative supercoiling in vivo is increased from a basal level of -sigma approximately 0.022 to -sigma approximately -0.052 by transcription-induced supercoiling. The induced supercoiling is very efficient, indicating that the tyrT promoter is itself contributing to the steady-state level despite a total lack of membrane anchorage for the tyrT transcription unit. This study provides a new example of the topological coupling of promoters.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=395530Documentos Relacionados
- Promoter mutations in the transfer RNA gene tyrT of Escherichia coli.
- PpGpp regulates the binding of two RNA polymerase molecules to the tyrT promoter.
- The tyrT locus of Escherichia coli B.
- T7 promoter contacts essential for promoter activity in vivo.
- A novel RNA product of the tyrT operon of Escherichia coli.