Fig. 5.

Transcription initiation at the tyrT promoter and utilization of DNA wrapping by FIS and RNA polymerase. Conversion of the DNA analog information into the digital code by transmission of the torque stored in the microloop stabilised at the tyrT gene promoter. Left-handed (lh) toroidal coils are metastable to right-handed (rh) plectonemic coils, activation involves conversion of the left-handed into a right-handed coil thus transmitting the supercoil energy to the promoter region and facilitating untwisting of the DNA at the transcription startpoint. a RNA polymerase binding. b Cooperative binding of transcriptional activator FIS to site I proximal to polymerase. c Cooperative binding of FIS to the upstream sites II and III and stabilization of the closed polymerase complex. d Untwisting of the transcription start site (promoter opening) and ejection of FIS at site II. e Escape of polymerase from the promoter and initiation of transcription generating the digital linear message. Right panel shows the AFM images of nucleoprotein complexes assembled at the E. coli tyrT promoter containing three FIS binding sites arranged in helical register and corresponding to depicted stages A and C (courtesy S. Maurer). Reproduced from Muskhelishvili and Travers (2013) with permission