The Escherichia coli proU promoter element and its contribution to osmotically signaled transcription activation.
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.
Mellies
J
J
Section of Microbiology, University of California, Davis 95616.
Brems
R
R
Villarejo
M
M
D026905:Amino Acid Transport Systems; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D001622:Betaine / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics*; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics*; D008969:Molecular Sequence Data; D009876:Operon / Q000235:genetics; D009997:Osmotic Pressure; D011401:Promoter Regions, Genetic / Q000235:genetics*; D015398:Signal Transduction; D014158:Transcription, Genetic
D026905:Amino Acid Transport Systems; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C031908:H-NS protein, bacteria; C060774:ProU protein, Bacteria; D001622:Betaine