Open AccessRate-limiting steps in RNA chain initiation.
Author(s) -
William R. McClure
Publication year - 1980
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.77.10.5634
Subject(s) - bacteriophage , rna polymerase , limiting , promoter , isomerization , lag , abortive initiation , biology , biophysics , escherichia coli , steady state (chemistry) , enzyme , chemistry , rna , biochemistry , gene , gene expression , mechanical engineering , computer network , computer science , engineering , catalysis
Promoter-specific lags in the approach to the steady-state rate of abortive initiation were observed when Escherichia coli RNA polymerase was added to initiate the reaction. The lag times were related to the time required for free enzyme and free promoter to combine and isomerize into a functionally active complex. The lag times measured for several bacteriophage and bacterial promoters differed widely (10 sec to several minutes) and in most cases corresponded to the rate-limiting step in the initiation process. The unique advantage in using the abortive initiation reaction to measure the lags was that the binding and isomerization steps in a simple two-state model could be quantitated separately. The separation of the contributions of both steps was effected by deriving an equation to describe the rate of formation of the active binary complex. Results from experiments based on the theory showed a linear relationship between the observed lag times and the reciprocal enzyme concentration. The slope and intercept of the equation yielded quantitative estimates of the binding and isomerization steps in initiation. The analysis was applied to the bacteriophage T7 A2 and D promoters to show the bases for the differences in in vitro initiation frequency that have been observed for these promoters.