The LysR-type transcriptional regulator CysB controls the repression of hslJ transcription in Escherichia coli

Abstract

The LysR-type transcriptional regulator (LTTR) CysB is a transcription factor inEscherichia colicells, where as a homotetramer it binds the target promoter regions and activates the genes involved in sulphur utilization and sulphonate-sulphur metabolism, while negatively autoregulating its own transcription. ThehslJgene was found to be negatively regulated by CysB and directly correlated with novobiocin resistance of the bacterium.cysBmutants showed upregulation of thehslJ : : lacZgene fusion and exhibited increased novobiocin resistance. In this study thehslJtranscription start point and the corresponding putativeσ70promoter were determined. ThehslJpromoter region was defined by employing differenthslJ–lacZoperon fusions, and transcription of thehslJgene was shown to be subject to both repression imposed by the CysB regulator and direct or indirect autogenous negative control. These two regulations compete to some extent but they are not mutually exclusive. CysB acts as a direct repressor ofhslJtranscription and binds thehslJpromoter region that carries the putative CysB repressor site. This CysB binding, apparently responsible for repression, is enhanced in the presence of the ligandN-acetylserine (NAS), hitherto considered to be a positive cofactor in CysB-mediated gene regulations. Interallelic complementation of characterized CysB mutants I33N and S277Ter partially restored the repression ofhslJtranscription and the consequent novobiocin sensitivity, but did not complement the cysteine auxotrophy.