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?4), and diminished over time until, after 90?min, no difference in LEE operon promoter activity was observed between organisms treated with LacNAc-BSA or underivatized BSA (data not shown). The LacNAc-BSA-induced alteration of LEE promoter activity was BfpF-dependent because we detected no significant difference in LEE promoter activity in the strain UMD916 exposed to LacNAc-BSA (Fig.?4B), a phenotype that was restored to that of the wild-type E2348/69 strain by adding back a functional bfpF gene in trans http://www.selleckchem.com/products/Adrucil(Fluorouracil).html (Fig.?4C). To investigate if DegP activity was also required for BFP-retraction-mediated signalling, we introduced the pRMHlux1 to pRMHlux5 plasmids into ALN188, and monitored light production in the presence and absence of LacNAc-BSA. In these experiments, E2348/69 and ALN188 responded in a similar fashion to the presence of LacNAc-BSA, suggesting that bundlin degradation is not required for the LacNAc-BSA-induced alteration of LEE operon transcription rates (data not shown). MacRitchie and colleagues recently demonstrated that, similar to the effect of LacNAc-BSA-induced BFP retraction, activating the Cpx membrane stress-response system causes downregulation of LEE1, 2, 4 and 5 promoter activity, and slightly increased LEE3 promoter activity (Macritchie et?al., 2008). As the Cpx system is induced in response to misfolded or overexpressed proteins accumulating in the bacterial cell envelope (Raivio and Silhavy, 2001; Buelow and Raivio, 2005; Raivio, 2005), we investigated the effect of exposing E2348/69 to LacNAc-BSA on the promoter activity of two Cpx system genes, cpxP and degP. LacNAc-BSA significantly repressed both cpxP (P?