1887

Abstract

Sulfur oxidation in KCT001 is rendered by the combined action of several enzymes encoded by a thiosulfate-inducible operon. In this study it has been conclusively demonstrated by insertional mutagenesis that the regulatory gene of this operon is , which encodes a DNA-binding protein belonging to the ArsR-SmtB family. SoxR was found to bind to two promoter-operator segments within the cluster, of which the one () located between and controls the expression of sulfur-oxidation genes through while the other, a bi-directional element () located between and , controls the expression of in one direction and the putative regulatory cluster in the other. In the case of the promoter the repressor was found to bind in a cooperative manner to two distinct binding sites having different affinities, while in the case of the promoter binding occurred at a symmetric dimeric site and involved a higher degree of cooperativity. The high degree of cooperativity observed in the binding of SoxR to its target sites seemed to be due to the propensity of SoxR monomers to form dimers. The apparent dissociation constants of the SoxR–operator complexes were in the nanomolar range, indicating relatively strong interactions. It was demonstrated using a reporter system in that this high-affinity binding of SoxR led to efficient repression . Thus the role of SoxR as a repressor of the operon has not only been conclusively established but it has also been shown that this repression is brought about through cooperative interactions of SoxR with dimeric binding sites that occlude the operon promoters.

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2007-01-01
2019-10-14
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