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Figures
- Fig. 1.
Example of a basic two-component system. TheE. coli osmolarity-response system consists of an HPK osmosensor (EnvZ) and an RR transcription factor (OmpR) (Pratt and Silhavy, 1995). EnvZ autophosphorylates using ATP as the phosphate donor. The phosphate from the transmitter module of EnvZ is then transferred to an Asp residue in the receiver module of OmpR, thereby affecting the promoter interactions of the OmpR DNA-binding module, which regulates the transcription of two porin genes,ompF and ompC. Changes in osmolarity are perceived by the amino-terminal module of EnvZ. In response to such changes, EnvZ changes the level of phosphorylated OmpR. The dotted lines depict intra-protein regulatory interactions. The dashed line depicts phosphorylation/dephosphorylation events. P, Phosphoryl group; H, His; D, Asp.
- Fig. 2.
Examples of diversity in the two-component system. In A and B, a cell-surface receptor or transport protein is responsible for direct binding/detection of a stimulus, and this information is then conveyed to the appropriate HPK via protein-protein interactions. A, Part of the E. coli chemotaxis signaling pathway, a system in which the CheA HPK phosphorylates either of two different RRs; the CheY RR promotes changes in swimming direction, whereas the CheB RR promotes sensory adaptation (Bourret et al., 1991; Stock et al., 1991). The location of the phosphorylation site in CheA is atypical in that it is located outside of the transmitter module (Parkinson and Kofoid, 1992). B, Basic elements of the E. coli Pho(phosphate) system, which is responsible for controlling gene expression in response to phosphate availability. In this system, two distinct HPKs, PhoR and CreC, can phosphorylate the RR transcription factor PhoB. CreC responds to the intracellular concentration of some unknown metabolite, whereas PhoR is regulated by a phosphate-specific transport system (Wanner, 1994). C, BvgS, a hybrid HPK that regulates expression of virulence determinants of the human pathogen Bordetella pertussis in response to as-yet-unknown host factors. BvgS undergoes His to Asp to His phosphotransfer prior to phosphorylation of the RR transcription factor BvgA (Uhl and Miller, 1996). H, His; P, phosphoryl group; D, Asp.
Tables
Organism Probable Signal Pathway Output Signaling References Hybrid HPK (His→Asp) RR (→Asp) S. cerevisiae Osmolarity SLN1 YPD1 (→His) SSK1 MAPK cascade Maeda et al. (1994); Posas et al. (1996) S. pombe Various stresses ? MCS4 MAPK cascade Shieh et al. (1997) A. thaliana Ethylene ETR1 ? MAPK cascade (?) Chang et al. (1993); Hua et al. (1995); Hua et al. (1997) ERS-a ? MAPK cascade (?) ETR2 ? MAPK cascade (?) EIN4 ? MAPK cascade (?) D. discoideum Osmolarity DOKA ? Cytoskeletal alteration (?) Schuster et al. (1996) Secreted peptide DHKA REGA cAMP-dependent protein kinase activity Wang et al. (1996); Shaulsky et al. (1996); Shaulsky et al. (1998) -
↵F0-a A typical (not a hybrid) HPK.
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- Article
- SENSORY-RESPONSE CIRCUITS: REALITY CHECKS AT THE CELLULAR LEVEL
- BASIC PLAYERS: IT TAKES TWO TO SIGNAL
- LESSONS LEARNED FROM BACTERIAL TWO-COMPONENT SYSTEMS
- EUKARYOTIC TWO-COMPONENT SYSTEMS
- TWO-COMPONENT REGULATORS IN HIGHER PLANTS
- DIVERSITY IN SIGNALING OUTPUT
- SUMMARY
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