The Global Regulator Spx Functions in the Control of Organosulfur Metabolism inBacillus subtilis

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Abstract
Spx is a global transcriptional regulator of the oxidative stress response inBacillus subtilis. Its target is RNA polymerase, where it contacts the α subunit C-terminal domain. Recently, evidence was presented that Spx participates in sulfate-dependent control of organosulfur utilization operons, including theytmI,yxeI,ssu, andyrrToperons. TheyrrToperon includes the genes that function in cysteine synthesis fromS-adenosylmethionine through intermediatesS-adenosylhomocysteine, ribosylhomocysteine, homocysteine, and cystathionine. These operons are also negatively controlled by CymR, the repressor of cysteine biosynthesis operons. All of the operons are repressed in media containing cysteine or sulfate but are derepressed in medium containing the alternative sulfur source, methionine. Spx was found to negatively control the expression of these operons in sulfate medium, in part, by stimulating the expression of thecymRgene. In addition, microarray analysis, monitoring ofyrrT-lacZfusion expression, and in vitro transcription studies indicate that Spx directly activatesyrrToperon expression during growth in medium containing methionine as sole sulfur source. These experiments have uncovered additional roles for Spx in the control of gene expression during unperturbed, steady-state growth.

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