Free RNA polymerase and modeling global transcription in Escherichia coli.
Growth rate-dependent changes in the cytoplasmic concentration of free functional RNA polymerase, [R(f)], affect the activity of all bacterial genes. Since [R(f)] is not accessible to direct experimental quantitation, it can only be found indirectly from an evaluation of promoter activity data. Here, a theory has been derived to calculate [R(f)] from the concentrations of total RNA polymerase and promoters in a model system with known Michaelis-Menten constants for the polymerase-promoter interactions. The theory takes transcript lengths and elongation rates into account and predicts how [R(f)] changes with varying gene dosages. From experimental data on total concentrations of RNA polymerase and kinetic properties of different classes of promoters, the theory was developed into a mathematical model that reproduces the global transcriptional control in Escherichia coli growing at different rates. The model allows an estimation of the concentrations of free and DNA-bound RNA polymerase, as well as the partitioning of RNA polymerase into mRNA and stable RNA synthesizing fractions. According to this model, [R(f)] is about 0.4 and 1.2 microM at growth rates corresponding to 1.0 and 2.5 doublings/h, respectively. The model accurately reflects a number of further experimental observations and suggests that the free RNA polymerase concentration increases with increasing growth rate.
Bremer
H
H
Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, TX 75083-0688, USA.
Dennis
P
P
Ehrenberg
M
M
D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D007700:Kinetics; D008957:Models, Genetic; D011401:Promoter Regions, Genetic / Q000235:genetics; D014158:Transcription, Genetic / Q000235:genetics*
D004269:DNA, Bacterial; D012321:DNA-Directed RNA Polymerases