Faster growing cells must synthesize proteins more quickly. Increased ribosome abundance during faster growth in the bacterium Escherichia coli partly accounts for this speedup. Biogenesis of ribosomes must also increase correspondingly, which begins with transcription of rrn operons, the genes that transcribe ribosomal RNA (rRNA) which comprise 65% of a ribosome. RNA polymerase (RNAP), responsible for all DNA transcription, initiates this process. While systems biology studies show pronounced up-regulation of RNAP during faster growth, and structural biology experiments and modeling show that RNAP bind to DNA without specificity, neither approach can explain experimental observation that RNAP preferentially locates to specific operons during faster growth, despite the fact that RNAP has no chemical specificity for those genes. We demonstrate the underlying physics-based mechanism driving this process, and that colloidal-scale physics drive organization a whole-cell scale to help regulate growth rate.
