Notes from Papers.doc

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The soxRS locus of E.coli regulates an oxidative stress response that includes at least 10 genes involved in counteracting oxidative damage and in providing resist- ance to multiple antibiotics (Hidalgo and Demple, 1996b). The soxRS response is triggered when cells are exposed to nitric oxide (NO•) or to superoxide (O2•–)-generating agents such as paraquat (PQ) (Ama´ bile-Cuevas and Demple, 1991; Wu and Weiss, 1991; Nunoshiba et al., 1992; Nunoshiba et al., 1993). SoxR protein is evidently the sensor for this response (Nunoshiba et al., 1992; Wu and Weiss, 1992). Activated SoxR protein, a homodimer of 17 kDa subunits containing a pair of [2Fe–2S] clusters (Hidalgo et al., 1995; Wu et al., 1995), triggers expression

Two striking features of this SoxR–soxS interaction are the unusually long spacing between the –10 and –35 149 promoter elements and the position of the SoxR binding site.

Previous studies showed that soxS promoter sequences as short as ~180 bp are enough for full activation by RNAP and SoxR in vitro. However, the shortest version of the soxS promoter that we have assayed for activity in vivo by fusion to the lacZ gene is a 500 bp long segment that encompasses the whole soxRS intergenic promoter

Studies of many E.coli promoters have suggested that spacer length, rather than specific nucleotide sequence, intrinsic activity of otherwise similar promoters depends only on fluctuations of the spacer distance.

The first transcriptional event in the response to superoxide or nitric oxide stress in E.coli involves the interaction of activated SoxR with the promoter of the second regulatory gene, soxS. W

NO is a deliberate cytotoxic product of activated macrophages, along with other reactive oxygen species such as hydrogen peroxide (H2O2) and superoxide (O2-). Escherichia coli has a complex set of responses to H2O2 and O2- that involves approximately 80 inducible proteins;

We show here that a multigene system controlled by the redox-sensitive transcriptional regulator SoxR is activated by NO in vivo. This induction confers bacterial resistance to activated murine macrophages with kinetics that parallel the production of NO by these cells. Elimination of specific SoxR-regulated genes diminishes the resistance of these bacteria to the cytotoxic macrophages.

These results demonstrate that SoxR is a sensor for cellular exposure to NO, and that the soxRS response system may contribute to bacterial virulence.