Figure 2.
Multiple levels of regulation affect availability of the RpoS (σS) general stress response sigma factor in E. coli. The major regulators of RpoS synthesis and function are outlined here. Transcription is primarily from the prpoS promoter, embedded within the upstream nlpD gene. The resulting transcript includes a long 5′ UTR, which folds back to occlude ribosome entry. sRNAs, made in response to specific signals (see Fig. 3 and text), open this structure, promoting translation. Other stress signals lead to synthesis of anti-adaptors (green shapes) that block the rapid degradation of RpoS. When levels of RpoS (yellow spheres, σS) rise as a consequence of these changes in regulation, RpoS combines with core RNA polymerase (blue), inducing transcription of the genes of the RpoS regulon; Crl helps to promote RpoS capture of core polymerase.