Theoretical analysis of single-round transcription experiments on trp leader region

A kinetic model is proposed to reproduce the time courses of the concentration change in paused leader RNA, terminated leader RNA, and readthrough RNA in the single-round transcription experiments on trp leader region of Escherichia coli and its mutants, L132, L75, and L75L135 (Winkler, M. E., and C. Yanofsky, 1981, Biochemistry, 20:3738-3744; Fisher, R., and C. Yanofsky, 1983, J. Biol. Chem., 258:9208-9212). This model fits the experimental results well and also captures the essential aspects of the processes of transcriptional pausing and termination. In the wild type template, under optimal conditions, it is found that the transcription rate at the pause and attenuation sites is of the same order of magnitude, 10,000-fold lower than the transcription rate at the other sites, and the high termination level at the attenuation site is attributable to a higher dissociation rate. This analysis also provides a clue as to how the template base change, various concentrations of ribonucleoside triphosphates, and the presence or absence of L-factor affect the transcription and dissociation rates to yield different termination levels at the pause or attenuation site. It also discusses the molecular mechanism of the transcriptional pausing and termination.