Figure 1.

Schematic of the corA leader mRNA. The Salmonella corA leader can adopt two mutually exclusive conformations, stem-loops A+B or C+D, that control transcription elongation into the corA coding region by modulating accessibility of a rut site (3). Stem-loop A may not form in vivo due to translation of the overlapping ORF corL (dashed black box denotes corL start and stop codons) (3). Major sites of in vitro RNAP pausing (green) and Rho-dependent termination (blue) are denoted. In this work, we identify an additional RNA structure, stem-loop E (orange), whose formation may be independent of stem-loops B versus C+D. Stem-loops C+D suppress RNAP pausing at U240 (red star). Stem-loop E prevents Rho from triggering transcription termination at U192 (green star).