  In fast growing bacteria, ribosomal RNA (rRNA) is required to be transcribed
at very high rates to sustain the high cellular demand on ribosome synthesis.
This results in dense traffic of RNA polymerases (RNAP). We developed a
stochastic model, integrating results of single-molecule and quantitative in
vivo studies of E. coli, to evaluate the quantitative effect of pausing,
termination, and antitermination on rRNA transcription. Our calculations reveal
that in dense RNAP traffic, spontaneous pausing of RNAP can lead to severe
"traffic jams", as manifested in the broad distribution of inter-RNAP distances
and can be a major factor limiting transcription and hence growth. Our results
suggest the suppression of these pauses by the ribosomal antitermination
complex to be essential at fast growth. Moreover, unsuppressed pausing by even
a few non-antiterminated RNAPs can already reduce transcription drastically
under dense traffic. However, the termination factor Rho can remove the
non-antiterminated RNAPs and restore fast transcription. The results thus
suggest an intriguing role by Rho to enhance rather than attenuate rRNA
transcription.
