FIG 1 .

(A) Map of the algT/U operon. Arrows indicate promoters. (B) Model for the “activation” of σ²² activity by regulated intramembrane proteolytic (RIP) degradation of the anti-sigma factor MucA. Under nonstress conditions, σ²² activity is low due to its sequestration at the inner membrane by the MucA-MucB complex. In response to cell wall stress (e.g., d-cycloserine), AlgW cleaves MucA in the C terminus and then RseP (YaeL) and ClpXP cleave the MucA N-terminal region, releasing σ²² from posttranslational repression. This allows σ²² to complex with core RNA polymerase, thus increasing transcription of target promoters in the σ²² stimulon, which includes PalgD of the alginate biosynthetic operon. Abbreviations: OM, outer membrane; PG, peptidoglycan; IM, inner membrane.