A connecter-like factor, CacA, links RssB/RpoS and the CpxR/CpxA two-component system in Salmonella

Abstract

Background: Bacteria integrate numerous environmental stimuli when generating cellular responses. Increasing numbers of examples describe how one two-component system (TCS) responds to signals detected by the sensor of another TCS. However, the molecular mechanisms underlying this phenomenon remain poorly defined. Results: Here, we report a connector-like factor that affects the activity of the CpxR/CpxA two-component system in Salmonella enterica serovar Typhimurium. We isolated a clone that induced the expression of a cpxP-lac gene fusion from a high-copy-number plasmid pool of random Salmonella genomic fragments. A 63-amino acid protein, CacA, was responsible for the CpxA/CpxR-dependent activation of the cpxP gene. The CpxR-activated genes cpxP and spy exhibited approximately 30% and 50% reductions in transcription, respectively, in a clean cacA deletion mutant strain in comparison to wild-type. From 33 response regulator (RR) deletion mutants, we identified that the RssB regulator represses cacA transcription. Substitution mutations in a conserved -10 region harboring the RNA polymerase recognition sequence, which is well conserved with a known RpoS -10 region consensus sequence, rendered the cacA promoter RpoS-independent. The CacA-mediated induction of cpxP transcription was affected in a trxA deletion mutant, which encodes thioredoxin 1, suggesting a role for cysteine thiol-disulfide exchange(s) in CacA-dependent Cpx activation. Conclusions: We identified CacA as an activator of the CpxR/CpxA system in the plasmid clone. We propose that CacA may integrate the regulatory status of RssB/RpoS into the CpxR/CpxA system. Future investigations are necessary to thoroughly elucidate how CacA activates the CpxR/CpxA system.

Analysis of the Salmonella regulatory network suggests involvement of SsrB and H-NS in σE-regulated SPI-2 gene expression

“…Consistent with previous findings that the phage shock protein (Psp) system and two-component regulatory system CpxR/CpxA compensate for the loss of σ E function, we found that genes in the psp operon, including pspA, pspB, pspD , and pspE , were up-regulated in ΔrpoE under LPM 20 h condition when compared to WT (Figure 3D ) (Connolly et al, 1997 ; Becker et al, 2005 ). The expression of cpxP , an indicator of the activation status of the CpxR/CpxA system, was also found to be elevated in ΔrpoE when compared to WT in LPM 4 h and 20 h samples (Figure 3D ) (Kato et al, 2012 ). Moreover, σ E up-regulated the cold-shock protein genes cspA , cspC , and cspE ; the universal stress genes uspA and ynaF ; the oxidative stress-response genes sodA, sodB, and sodC_2 ; the hyperosmotic stress genes osmC, osmE, and osmY ; and the heat shock protein genes ibpA and ibpB under LB log phase condition.…”

MifM-instructed translation arrest involves nascent chain interactions with the exterior as well as the interior of the ribosome

“…5A and Supplementary Fig. S1 was performed as described previously 56 , 57 with the following modifications. B. subtilis cells were grown at 37 °C for 120–150 min in LB medium with (Fig.…”

Identification and characterization of a translation arrest motif in VemP by systematic mutational analysis

“…LacZ activity of the cells expressing DSSVemP'-'LacZ was measured basically according to the procedure published previously (18). The standard procedure is as follows.…”

“…Clearly, the cells expressing the frame-shifted protein did not produce any arrested product even in the sec-deficient condition (Fig. 1B, lanes [16][17][18]. We also examined the effects of five synonymous mutations at the Leu-153 residue in the conserved region on the elongation arrest efficiency using a new reporter system described in the following section (results are shown in Fig.…”