Nucleic Acids Research, 1984, Vol. 12, No. 13 5287-5306
© 1984
MOLECULAR BIOLOGY |
Kinetics of RNA polymerase-promoter complex formation: effects of nonspecific DNA-protein interactions
Department of Biochemistry, Michigan State University East Lansing, MI 48824, USA
Received April 23, 1984. Accepted June 15, 1984.
The rates of formation of RNA polymerase-promoter open complexes at the galactose P2 and lactose UV5 promoters of E. coli were studied using polyacrylamide gels to separate the heparin-resistant complexes from unbound DNA. Both the apparent rate and extent of reaction at these promoters are inhibited at excess RNA polymerase. This inhibition, which can be relieved by the addition of non-promoter DNA, is interpreted to be the result of occulsion of the promoter site by nonspecifically bound polymerase. Additionally, biphasic kinetics are observed at both gal P2 and lac UV5. but not at the PR promoter of phage A. This behavior disappears when the concentration of RNA polymerase in the binding reaction is less than that of the promoter fragment. It is proposed that at excess enzyme nonspecifically bound polymerase molecules sliding along the DNA may "bump" closed complexes from the promoter site thereby reducing the rate of open complex formation. Kinetics mechanisms quantifying both the occlusion and bumping phenomena are presented.
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