Demonstration that the TyrR protein and RNA polymerase complex formed at the divergent P3 promoter inhibits binding of RNA polymerase to the major promoter, P1, of the aroP gene of Escherichia coli.
In previous studies, we have identified three promoters (P1, P2, and P3) in the regulatory region of the Escherichia coli aroP gene (P. Wang, J. Yang, and A. J. Pittard, J. Bacteriol. 179:4206-4212, 1997). Both P1 and P2 can direct mRNA synthesis for aroP expression, whereas P3 is a divergent promoter which overlaps with P1. The repression of transcription from the major promoter, P1, has been postulated to involve the activation of the divergent promoter, P3, by the TyrR protein (P. Wang, J. Yang, B. Lawley, and A. J. Pittard, J. Bacteriol. 179:4213-4218, 1997). In the present study, we confirmed the proposed mechanism of P3-mediated repression of P1 transcription by studying the binding of RNA polymerase to the promoters P1 and P3 in vitro in the presence and absence of TyrR protein and its cofactors. Our results show that (i) only one RNA polymerase molecule can bind to the DNA fragment carrying the aroP regulatory region, (ii) RNA polymerase has a higher affinity for P1 than for either P2 or P3 and binds to P1 in the absence of TyrR protein, (iii) in the presence of TyrR protein and its cofactor, phenylalanine or tyrosine, RNA polymerase preferentially binds to P3, and (iv) RNA polymerase does not respond to the activation-defective mutant TyrR protein TyrR-RQ10 and remains bound to P1 in the presence of TyrR-RQ10 and either of the cofactors.
Department of Microbiology, University of Melbourne, Parkville, Victoria 3052, Australia.
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Ishihama
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Pittard
D026905:Amino Acid Transport Systems; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics*; D018983:DNA Footprinting; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010649:Phenylalanine / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012097:Repressor Proteins / Q000378:metabolism*; D014158:Transcription, Genetic; D014443:Tyrosine / Q000494:pharmacology
D026905:Amino Acid Transport Systems; C063201:AroP protein, E coli; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D012097:Repressor Proteins; C069256:TyrR protein, E coli; D014443:Tyrosine; D010649:Phenylalanine; D012321:DNA-Directed RNA Polymerases