Abstract
Bacillus subtilis SigW is localized to the cell membrane and is inactivated by the tight interaction with anti-sigma RsiW under normal growth conditions. Whereas SigW is discharged from RsiW binding and thus initiates the transcription of its regulon under diverse stress conditions such as antibiotics and alkaline shock. The release and activation of SigW in response to extracytoplasmic signals is induced by the regulated intramembrane proteolysis of RsiW. As a ZAS (Zinc-containing anti-sigma) family protein, RsiW has a CHCC zinc binding motif, which implies that its anti-sigma activity may be regulated by the state of zinc coordination in addition to the proteolytic cleavage of RsiW. To understand the regulation mode of SigW activity by RsiW, we determined the crystal structures of SigW in complex with the cytoplasmic domain of RsiW, and compared the conformation of the CHCC motif in the reduced/zinc binding and the oxidized states. The structures revealed that RsiW inhibits the promoter binding of SigW by interacting with the surface groove of SigW. The interaction between SigW and RsiW is not disrupted by the oxidation of the CHCC motif in RsiW, suggesting that SigW activity might not be regulated by the zinc coordination states of the CHCC motif.
Highlights
In bacteria, gene transcription is initiated by sigma factor that mediates the recruitment of core RNA polymerase to a promoter region [1]
Anti-sigma RsiW in B. subtilis inhibits the SigW activity required for the transcription initiation of stress response genes [7, 8]
The cytoplasmic anti-sigma domain in RsiW has a CHCC motif for zinc coordination [18, 38], as a ZAS family protein that may be involved in the activity regulation of sigma factor through zinc coordination
Summary
Gene transcription is initiated by sigma factor that mediates the recruitment of core RNA polymerase to a promoter region [1]. Almost all bacteria harbor multiple sigma factors, including house-keeping and additional alternative sigma factors, each of which controls the transcription of its own regulon. While a housekeeping sigma factor regulates the expression of the majority genes for bacterial homeostasis, alternative sigma factors are suppressed to a basal level by a corresponding anti-sigma factor under normal growth conditions [2]. Each alternative sigma factor is activated in response to a cognate environmental change and induces the expression of a group of genes that permit adaptation to the altered environment [2].
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