Transcriptional co-activation at the ansB promoters: involvement of the activating regions of CRP and FNR when bound in tandem.
Previous work with semi-synthetic promoters containing a single CRP binding site centred at 41.5 bp from the transcription start site has demonstrated enhanced transcription (synergism) when a second binding site, for CRP or FNR, is placed upstream at around -91 bp. The ansB promoter in Escherichia coli is co-activated in a co-dependent manner by one dimer each of CRP and FNR protein whose binding sites are at around -91 and -41 bp, respectively, from the transcription start site. Similarly, the homologous ansB promoter in Salmonella is co-activated by two dimers of CRP which function synergistically. The binding sites at the E. coli promoter have been changed by mutation to provide a number of active promoter derivatives carrying other combinations of FNR and CRP binding sites. The co-dependent versus synergistic interaction of these activators and their requirement for known activating regions have been examined. The results demonstrate that FNR can co-activate when located upstream at around -91 bp in combination with either FNR or CRP downstream. When FNR occupies the downstream site the promoter is co-dependent on an upstream activator, but not when CRP occupies this site. Activating region 1 in CRP (defined by substitutions at residue H159) and its putative equivalent in FNR (defined by substitutions at S73) are mainly required in the upstream activator; the putative equivalent in FNR of activating region 3 of CRP (defined by substitutions at G85 and K52, respectively) is mainly required in the dimer which binds downstream. Activating region 1 of FNR is required only in the downstream subunit of the upstream activator in a promoter which is co-dependent on two FNR dimers. These data suggest that both bound upstream and downstream activators interact with RNA polymerase to promote transcription, and that co-dependence is determined by the nature of the activator plus the promoter context.
Scott
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Faculty of Science and Technology, Griffith University, Nathan, Brisbane, Queensland, Australia.
Busby
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Beacham
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D001215:Asparaginase / Q000235:genetics* / Q000502:physiology; D001426:Bacterial Proteins / Q000737:chemistry / Q000502:physiology*; D001483:Base Sequence; D002352:Carrier Proteins; D002373:Cyclic AMP Receptor Protein / Q000737:chemistry / Q000502:physiology*; D012321:DNA-Directed RNA Polymerases; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000502:physiology*; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011487:Protein Conformation; D015533:Transcriptional Activation; D001616:beta-Galactosidase / Q000235:genetics
D001426:Bacterial Proteins; D002352:Carrier Proteins; D002373:Cyclic AMP Receptor Protein; D029968:Escherichia coli Proteins; C060704:FNR protein, E coli; D007506:Iron-Sulfur Proteins; D012321:DNA-Directed RNA Polymerases; D001616:beta-Galactosidase; D001215:Asparaginase