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As seen in Figure ?Figure3C3C, the addition of ATc had no apparent impact on the protein profile of the control strain, while the addition of ATc to WAirR resulted in a stronger detection of a protein band similar in size to the SspB zymogen at 44 kD. Additionally, many protein bands were absent in the stained SDS-PAGE from the induced WAirR supernatant, consistent with previous reports that up-regulation of SspB (and SspA) results in degradation of other exported proteins (Karlsson et al., 2001; Jones et al., 2008). As a positive control, the sspB gene was cloned into the same ATc inducible expression vector (pSspB, strain WSspB). Further confirmation of SspB up-regulation was carried out by immunoblotting using chicken egg antibody specific for SspB (Kolar et al., 2013). In the control strain, SspB production was low and appeared unaffected by the addition of ATc (Figure ?Figure3D3D). In an ATc dose-dependent manner, staphopain B production was up-regulated in the WAirR supernatant (Figure ?Figure3D3D). SspB was readily detectable in the induced positive control WSspB supernatant as well. The SspB specific antibody detected the various processed and degraded forms of the protein (Shaw et al., 2005, 2004). These data clearly indicate a regulatory link between AirSR and SspB production. Transcription from the ssp Promoter is Regulated by AirR Staphopain B is produced from the middle gene of a three gene operon and is bordered upstream by sspA, encoding the V8 serine endopeptidase and downstream by sspC which encodes staphostatin B, a cytoplasmic inhibitor of SspB (Rice et al., 2001). To determine if the up-regulation of SspB production occurs post-transcriptionally or if transcription from the ssp promoter is increased in the induced WAirR strain, we examined the PDGFRB effect of AirR overproduction and deletion of airSR on the transcription of the ssp operon using a ssp promoter-luxABCDE reporter system. The induction of AirR production with inducer ATc resulted in a fivefold maximal increase in bioluminescence intensity compared to the control (Figure ?Figure4A4A). Furthermore, bioluminescence driven by the ssp promoter was higher and sustained throughout the growth of WAirR, demonstrating that continued and prolonged AirR overproduction results in increased transcription from the ssp promoter (Figure ?Figure4A4A). To examine if the absence of AirSR impacts the ssp promoter driven bioluminescence, the ssp-lux reporter was electroporated into the wild-type AH1263 and ��airSR, AH2084, strains. Maximum ssp-driven bioluminescence was reduced fivefold in AH2084 compared to AH1263 (Figure ?Figure4B4B). These data indicate AirSR is a positive transcriptional regulator of the sspABC operon.