The Escherichia coli proU promoter element and its contribution to osmotically signaled transcription activation.

AUTOR(ES)

Mellies, J

RESUMO

The proU operon of Escherichia coli encodes a high-affinity glycine betaine transport system which is osmotically inducible and enables the organism to recover from the deleterious effects of hyperosmotic shock. Regulation occurs at the transcriptional level. KMnO4 footprinting showed that the preponderance of transcription initiated at a single primary promoter region and that proU transcription activation did not occur differentially at alternate promoters in response to various levels of salt shock. Mutational analysis confirmed the location of the primary promoter and identified an extended -10 region required for promoter activity. Specific nucleotides within the spacer, between position -10 and position -35, were important for maximal expression, but every mutant which retained transcriptional activity remained responsive to osmotic signals. A chromosomal 90-bp minimal promoter fragment fused to lacZ was not significantly osmotically inducible. However, transcription from this fragment was resistant to inhibition by salt shock. A mutation in osmZ, which encodes the DNA-binding protein H-NS, derepressed wild-type proU expression by sevenfold but did not alter expression from the minimal promoter. The current data support a model in which the role of the proU promoter is to function efficiently at high ionic strength while other cis-acting elements receive and respond to the osmotic signal.

Documentos Relacionados

• Site-directed mutational analysis of the osmotically regulated proU promoter of Salmonella typhimurium.
• Evidence for transcription attenuation rendering cryptic a sigmaS-dependent promoter of the osmotically regulated proU operon of Salmonella typhimurium.
• A transcriptional silencer downstream of the promoter in the osmotically controlled proU operon of Salmonella typhimurium.
• DNA twist, flexibility and transcription of the osmoregulated proU promoter of Salmonella typhimurium.
• Nucleotide sequence of the osmoregulatory proU operon of Escherichia coli.