Figure 1. NanoRNA-mediated priming alters transcription start site selection in Escherichia coli. (A) Transcription start sites observed at promoters targeted by nanoRNA-mediated priming. (B) Model to account for the differential susceptibility of –1/+1 TA promoters to nanoRNA-mediated priming. Depicted is the competition between NTPs (purple) and the dinucleotide UA (red) for use by RNAP during initiation at a –1/+1 TA promoter. The abundance of transcripts generated by de novo initiation is greater than the abundance of transcripts that are generated by priming with UA. The steady-state levels of transcripts reflect the relative stability of those transcripts generated by nanoRNA-mediated priming compared with those generated by de novo initiation. At the majority of –1/+1 TA promoters (non-targeted) the stability of transcripts generated by nanoRNA-mediated priming is less than or equal to the stability of transcripts generated by de novo initiation. At the targeted promoters the stability of transcripts generated by nanoRNA-mediated priming is significantly greater than the stability of transcripts generated by de novo initiation.