Dual regulation of open-complex formation and promoter clearance by Arc explains a novel repressor to activator switch.
In studies of variants of the P(ant) promoter of bacteriophage P22, the Arc protein was found not only to slow the rate at which RNA polymerase forms open complexes but also to accelerate the rate at which the enzyme clears the promoter. These dual activities permit Arc, bound at a single operator subsite, to act as an activator or as a repressor of different promoter variants. For example, Arc activates a P(ant) variant for which promoter clearance is rate limiting in the presence and absence of Arc but represses a closely related variant for which open-complex formation becomes rate limiting in the presence of Arc. The acceleration of promoter clearance by Arc requires occupancy of the operator subsite proximal to the -35 region and is diminished when Arc bears a mutation in Arg-23, a residue that makes a DNA-backbone contact in the operator complex.
Smith
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Department of Biology, Massachusetts Institute of Technology, Cambridge 02139-4703, USA.
Sauer
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RT
D018983:DNA Footprinting; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics* / Q000821:virology; D015964:Gene Expression Regulation, Bacterial; D014644:Genetic Variation; D007700:Kinetics; D009875:Operator Regions, Genetic; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014764:Viral Proteins / Q000378:metabolism*; D054334:Viral Regulatory and Accessory Proteins
D012097:Repressor Proteins; D014157:Transcription Factors; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins; C016649:phage repressor proteins; D012321:DNA-Directed RNA Polymerases