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RpoS is an alternative sigma-70 family (group 2) sigma factor that binds core RNA polymerase and redirects transcription to promoters supporting survival during stationary phase and the general stress response.
"RpoS is an alternative sigma factor** (sigma-70 family; “group 2” sigma) that binds the **core RNA polymerase** and redirects transcription to a broad set of promoters that support survival during **stationary phase** and diverse stresses—commonly termed the **general stress response (GSR)**"
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RpoS does not catalyze a biochemical reaction and is not a transporter; its primary function is sequence-specific transcription initiation control.
"RpoS does **not** catalyze a biochemical reaction and is **not** a transporter. Its primary function is **sequence-specific transcription initiation control**"
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As a group 2 sigma factor RpoS binds core RNAP and recognizes promoters similar to RpoD, supporting annotation as sigma S rather than an enzyme or transporter.
"as a group 2 sigma factor, it binds core RNAP and recognizes promoters similar to RpoD"
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RpoS competes with the housekeeping sigma RpoD for a limiting pool of core RNA polymerase (sigma competition), framing a growth-versus-survival tradeoff.
"A central concept is **sigma competition**: RpoS competes with the housekeeping sigma **RpoD (σ70)** and other alternative sigmas for a limiting pool of core RNAP."
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RpoS is a cytosolic transcription factor that exerts its function by interacting with cytosolic RNA polymerase and promoter DNA.
"RpoS is a **cytosolic** transcription factor (sigma factor) that exerts its function by interacting with **cytosolic RNA polymerase** and promoter DNA."
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RpoS-dependent regulons increase tolerance to oxidative, osmotic, temperature, and pH stress and other stationary-phase threats.
"RpoS-dependent regulons typically include genes that increase tolerance to oxidative stress, osmotic stress, temperature and pH extremes, and other stationary-phase threats."
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In KT2440, RsmA directly binds the rpoS mRNA ribosome-binding site and start codon (confirmed by EMSA), supporting post-transcriptional control of RpoS levels via the Gac/Rsm network.
"binding of RsmA to an RNA fragment containing the **ribosome-binding site and start codon** of rpoS was confirmed by **EMSA**"
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In KT2440, lapF transcription is dependent on RpoS and cfcR expression is regulated by RpoS, embedding RpoS in the c-di-GMP-controlled biofilm circuit.
"lapF transcription is described as dependent on RpoS in KT2440 biofilm literature"
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Stationary-phase induction does not always imply RpoS activation; the KT2440 K1-T6SS is induced in stationary phase but is not RpoS-dependent and is indirectly repressed by RpoS, defining a boundary of the RpoS regulon.
"K1-T6SS is induced in stationary phase but is not RpoS-dependent and is indirectly repressed by RpoS"