Department of Biochemistry, Colleges of Medicine and Liberal Arts and Sciences, University of Illinois, Urbana, IL 61801, USA
Correspondence
George W. Ordal
g-ordal{at}uiuc.edu
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ABSTRACT |
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INTRODUCTION |
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Adaptation, which brings the levels of CheA-P and CheY-P back to prestimulus levels following addition of attractant, involves a coordinated methylation and demethylation of different sites on the receptors in B. subtilis (Zimmer et al., 2000) and involves only methylation of several possible sites in E. coli/Salmonella enterica (Terwilliger et al., 1986
). CheR methyltransferase carries out the methylation in these organisms (Burgess-Cassler et al., 1982
; Springer & Koshland, 1977
) and the CheB methylesterase, the demethylation (Goldman et al., 1984
; Stock & Koshland, 1978
). The B. subtilis chemotaxis mechanism is more elaborate than that of the paradigm organism E. coli and involves several proteins not found in E. coli CheC, CheD and CheV (Aizawa et al., 2001
; Fredrick & Helmann, 1994
; Karatan et al., 2001
; Kirby et al., 2001
; Kristich & Ordal, 2002
; Rosario & Ordal, 1996
; Rosario et al., 1995
). However, B. subtilis lacks CheZ, which in E. coli dephosphorylates CheY-P (Blat & Eisenbach, 1994
; Lukat & Stock, 1993
; Zhao et al., 2002
). CheD deamidates certain selected glutamine residues in the receptors, changing them to glutamate residues (Kristich & Ordal, 2002
), a reaction that makes the receptors more amenable to stimulation by attractant, possibly due to an effect on higher-order complexes within receptor clusters (Kirby et al., 2001
). The other two proteins CheC and CheV are involved in mechanisms of adaptation. CheV has two domains, a CheW-type coupling domain and a CheY-type response-regulator domain (Fredrick & Helmann, 1994
), which undergoes phosphorylation to help bring about adaptation (Karatan et al., 2001
). CheC works by an unknown mechanism. There is evidence that it can bind to the receptor complex, including the receptors, the CheA kinase and CheD, and it is homologous to a region within the switch proteins FliM and FliY (Kirby et al., 2001
). It has been suggested that CheC binds to one or both of these switch proteins (Kirby et al., 2001
). Interestingly, CheC and CheD interact (Rosario & Ordal, 1996
) but the purpose is unknown, for there are many bacteria that have cheD but lack cheC (Kirby et al., 2001
). A summary of the properties of the chemotactic proteins of B. subtilis is presented in Table 1
and a diagram of their proposed locations is given in Fig. 1
.
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METHODS |
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Construction of strains.
The strains studied in this article are given in Table 2. Strain OI3627, the cheRBCD mutant, was constructed by the same procedure as described by Kirby et al. (1999)
. The linkage of cheCD, as determined by Cmr, and unkU29 : : spc (due to integration of a Spcr cassette in an unknown gene upstream of the major fla/che operon), was 70 % by PBS1 transduction. Strain OI3642, the cheRBCDV mutant, was created by transducing OI3627 to Knr using PBS1 grown on HB4004, which contains a null mutation in cheV (Rosario et al., 1994
). Strain OI3511, the cheRBCDW mutant, was created in two stages. First, plasmid pC11 (Hanlon et al., 1992
), which contains part of cheA as well as cheW, cheC, cheD and part of sigD, was gutted of cheW, cheC and cheD, which was replaced with a terminatorless cat cassette (Bischoff & Ordal, 1991
) to make plasmid pK37. This plasmid was linearized and introduced into the cheB mutant OI2715 by transformation, with selection for Cmr, to make strain OI3512. Finally, strain OI2680 was made His+ by selection for histidine prototrophy, and the cheR allele was introduced into OI3512 by PBS1 transduction with selection for His+. Presence of the cheR allele was confirmed by growing PBS1 on candidates, transducing OI1085 to His+ and scoring for Cmr.
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RESULTS |
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Chemotactic behaviour of the cheBcheCcheD mutant
Behavioural responses of cheB and cheC mutants to addition and removal of asparagine have been reported (Kirby et al., 2000, 2001
). The cheB mutant could respond to high concentrations of asparagine (504 µM, corresponding to 90 % receptor occupancy: Ordal et al., 1977
). However, it was impaired in adaptation to this stimulus as well as its response to the removal (Kirby et al., 2000
; Zimmer et al., 2002
). The cheC mutant showed impaired adaptation to the addition of 504 µM asparagine, but normal response to its removal (Kirby et al., 2001
; Rosario et al., 1995
). To determine the behavioural responses of the cheBCD mutant, tethered-cell assays were performed with this concentration of asparagine. Previous analysis of rotational behaviour of the cheD and cheCD strains had indicated that only 50 % of the cells were capable of responding to the addition of asparagine in either of the strains (Kirby et al., 2001
). However, in the cheBCD mutant every cell analysed showed a response to the addition of asparagine (Fig. 2
). This strain was also able to partially adapt to the addition of asparagine.
Chemotactic behaviour generated by minimal systems
In order to determine the minimal chemotaxis system still capable of response and adaptation to a positive stimulus, three strains were constructed: cheRBCD (Kirby et al., 1999), cheRBCDW and cheRBCDV. The latter two strains each lack one of the two proteins that couple the CheA autokinase to the MCP receptor complex. A cheWV strain has a very tumbly bias and is unresponsive to all stimuli (Karatan et al., 2001
; Rosario et al., 1994
). The cheRBCD strain had a very low prestimulus CCW bias and was unresponsive to the addition and removal of asparagine (Fig. 3
), and the mean prestimulus CCW and CW event durations (Table 5
) were not significantly different from those of the other strains lacking CheD (Table 5
). Interestingly, further deletion of cheW restored the responsive nature of the chemotaxis system (Fig. 3
) and significantly increased the prestimulus CCW bias (Table 5
). This increase in bias was entirely due to an increase in the mean CCW event duration.
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DISCUSSION |
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The observation that the cheC mutant has reduced flagellar switching frequency suggests that CheC reduces the durations of CCW and CW events. This result is consistent with a reduction in the energy of activation for the transition between CCW and CW directions of flagellar rotation. One way this might occur would be by binding of CheC to FliY or FliM (see Kirby et al., 2001) and stabilizing a conformation of the switch proteins that is closer to the transition state. Kirby et al. (2001)
suggested that since CheC has similarity to switch proteins, it might transiently associate with the switch complex and since it binds to the receptors, CheD and CheA, it might go from the switch to the receptors as part of a mechanism of adaptation (cheC mutants adapt poorly: Kirby et al., 2001
; Rosario et al., 1995
). Our results support this hypothesis by showing that CheC does have an effect on switch properties and it is hard to imagine a way that such an effect can occur other than by direct binding.
Not only is it likely that CheC binds to the switch, but also two lines of evidence are consistent with the hypothesis that CheC is at least transiently associated with the ternary receptor complex. (i) CheC was shown to interact with the asparagine receptor McpB as well as CheA and CheD in a yeast two-hybrid assay (Kirby et al., 2001). (Both CheA and CheD interact with receptors directly: see Introduction.) (ii) It has also been shown that receptor methylation is affected by CheC because cheC mutants have overmethylated receptors (Rosario & Ordal, 1996
). Thus, not only is there evidence that CheC can interact at both the receptors and at the switch and hence might travel between them as part of a mechanism but also it is possible that the affinity of CheC for the receptors could be determined by the methylation state of the receptors.
In order to account for the effect of a null mutation in cheB on switching frequency (much shorter durations of CCW and CW rotations; see Table 3), two hypotheses are apparent. One is that CheB binds directly to the switch to affect switching frequency and the other is that in the cheB mutant, there is more CheC available to bind to the switch. We favour the latter hypothesis since there is no evidence that CheB, an enzyme that demethylates receptors, binds to the switch. By contrast, the effect of the cheB null mutation on switching frequency can be accounted for by assuming that overmethylated receptors have minimal affinity for CheC (see preceding paragraph). In this hypothesis, a surplus of CheC could result in increased binding at the switch and further lowering of the energy of activation of transition beyond that in wild-type, leading to the increased switching frequency observed in the cheB mutant.
This hypothesis that effects of different conditions (such as lack of CheB methylesterase) on switching frequency are mediated via CheC levels also may provide understanding of the incomplete adaptation for durations of CW and CCW rotation following addition of attractant (Table 4). It is generally accepted that bacteria fully adapt to stimuli (Alon et al., 1999
; Barkai & Leibler, 1997
; Macnab & Koshland, 1972
), and it is true that B. subtilis adapts fully in terms of bias (Table 4
). However, it does not adapt in terms of durations of CCW and CW rotations; in fact, both are longer after adaptation (Table 4
). No current model of chemotaxis accounts for this failure of adaptation. However, if we assume that the adapted receptor complex has increased affinity for CheC, then there would be less CheC binding at the switch and the switching frequency would be longer.
This line of thinking, where CheC binding to the switch affects switching frequency, might provide insight into a longstanding puzzle. Many archaea and some bacteria have CheC or the closely related CheX (Kirby et al., 2001). Some of these have polar flagella and, on negative stimuli, undergo repeated reversals of motion, such as the spirochaete Spirochaeta aurantia (Cercignani et al., 1998
; Fosnaugh & Greenberg, 1988
) and the archaeon Halobacterium salinarum (Spudich et al., 1989
). It is clear that the main output of the receptor/CheA complex is to regulate CheY-P levels in these as in all chemotactic bacteria/archaea but how CheY-P levels can regulate switching frequency (it primarily affects bias) has never been understood. In line with the effect of CheC on switching frequency in B. subtilis, we propose a possible mechanism for the increased switching frequency observed in these organisms upon negative stimulation, namely change in CheC (or CheX for S. aurantia) binding at the switch.
To make this argument, we first point out that that in the case of H. salinarum, at least, CheY-P has a similar function as in E. coli and B. subtilis in that it permits the non-default direction of flagellar rotation. In a cheY mutant of H. salinarum, only forward swimming (chronic CW rotation of the flagella at each end of the archeon) occurs (Rudolph & Oesterhelt, 1996). Backward swimming and reversals between directions, however, occur in wild-type. The increased reversals on negative stimulus might be due to changing CheY-P levels affecting affinity of CheC (or CheX) for the switch and possibly also to changing affinity for CheC (or CheX) at the receptors (due to methylation changes that occur there: Nordmann et al., 1994
; Spudich et al., 1989
). As a further parallel with B. subtilis, we note that a cheB mutant of H. salinarum shows increased frequency of reversals, with no effect on the ratio of CW and CCW rotation of the flagella, compared with wild-type (Rudolph & Oesterhelt, 1996
). Since in the B. subtilis cheB mutant the ratio of CW and CCW rotation (that is, bias) of the flagella is unchanged but switching frequency is increased (Table 3
), it is not hard to imagine that reversal frequency in H. salinarum and B. subtilis are controlled by the same mechanism, namely, amount of CheC bound at the switch.
One of the hallmarks of B. subtilis chemotaxis is that multiple adaptational mechanisms appear to operate concurrently. Besides the CheC mechanism, there is one that involves methylation/demethylation of the receptors (Hanlon & Ordal, 1994; Kirby et al., 1997
; Zimmer et al., 2000
, 2002
) and another that involves phosphorylation of the response regulator CheV (Karatan et al., 2001
). We sought to understand how deletion of these adaptational systems affected the unstimulated behaviour of bacteria and their response to attractant. We were already aware of the effect of deleting cheD and of the fact that the phenotype of the cheD and cheCD mutants was quite similar (considerably different from the cheC mutant) (Kirby et al., 2000
). We confirmed and extended this previous observation to include strains cheBCD, cheBCD, cheRBCDW and cheRBCDV. The low prestimulus biases that occur in these appear to be a result of reduced durations of mean CCW events due, probably, to receptors undeamidated by CheD (Kristich & Ordal, 2002
) being fairly inactive at stimulating the CheA kinase. Earlier work had also shown that in both the cheD and cheCD mutants about half the cells responded and half did not respond to addition of asparagine (Kirby et al., 2001
). We have shown here that this responsiveness was influenced by methylation in the sense that further deletion of cheB made the bacteria all responsive but, curiously, further deletion of cheR made all of them unresponsive. Obviously, the methylation system has a profound effect on the overall geometry and functioning of the receptor/kinase complex.
It should be noted that the failure of the cheRBCD mutant to respond to asparagine in the tethered-cell assay (or on swarm plates; data not shown) is in contrast to the results of Kirby et al. (1999), who reported that oscillations in CCW bias occurred on addition of attractant and stopped on its removal. Those results were reproducible; however, the linkage between cheD and a Spcr marker in an unidentified gene upstream of the beginning of the fla/che operon (Slack et al., 1995
) was later found to be tenfold lower than expected for unknown reasons. The conclusion of the paper that the adaptation was due to CheY-P feedback at the receptors may have been premature since at that time CheV was not recognized as an adaptational protein.
Interestingly, deletion of either gene encoding the coupling proteins cheW or cheV (Karatan et al., 2001; Rosario et al., 1994
) to make a cheRBCDW or cheRBCDV mutant made the bacteria again responsive to stimuli, and in the former strain also significantly increased the mean prestimulus CCW bias (Table 5
). In this sense cheW had a moderating effect on cheD, the only allele that we observed to have this effect. In some way, the conformation of the receptors/CheA complex was very stable in a refractory state when both coupling proteins were present and became more amenable to changing to an active state when one of the coupling proteins was deleted. Very interestingly, the cheRBCDV mutant lacked all known adaptation systems the methylation/demethylation mechanism, the CheV mechanism and the CheC mechanism and yet showed a progressive decrease in CCW bias following the response to the addition of attractant. Very recent experiments have revealed that FliY, one of the switch proteins, can catalyse dephosphorylation of CheY-P (Szurmant et al., 2003
) and in future experiments we will investigate the behavioural phenotype of mutants unable to carry out this dephosphorylation.
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ACKNOWLEDGEMENTS |
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REFERENCES |
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Alon, U., Camarena, L., Surette, M. G., Aguera y Arcas, B., Liu, Y., Leibler, S. & Stock, J. B. (1998). Response regulator output in bacterial chemotaxis. EMBO J 17, 42384248.
Alon, U., Surette, M. G., Barkai, N. & Leibler, S. (1999). Robustness in bacterial chemotaxis. Nature 397, 168171.[CrossRef][Medline]
Barkai, N. & Leibler, S. (1997). Robustness in simple biochemical networks. Nature 387, 913917.[CrossRef][Medline]
Berg, H. C. & Brown, D. A. (1972). Chemotaxis in Escherichia coli analysed by three-dimensional tracking. Nature 239, 500504.[Medline]
Bischoff, D. S. & Ordal, G. W. (1991). Sequence and characterization of Bacillus subtilis CheB, a homolog of Escherichia coli CheY, and its role in a different mechanism of chemotaxis. J Biol Chem 266, 1230112305.
Bischoff, D. S., Bourret, R. B., Kirsch, M. L. & Ordal, G. W. (1993). Purification and characterization of Bacillus subtilis CheY. Biochemistry 32, 92569261.[Medline]
Blat, Y. & Eisenbach, M. (1994). Phosphorylation-dependent binding of the chemotaxis signal molecule CheY to its phosphatase, CheZ. Biochemistry 33, 902906.[Medline]
Bourret, R. B. & Stock, A. M. (2002). Molecular information processing: lessons from bacterial chemotaxis. J Biol Chem 277, 96259628.
Bren, A. & Eisenbach, M. (1998). The N terminus of the flagellar switch protein, FliM, is the binding domain for the chemotactic response regulator, CheY. J Mol Biol 278, 507514.[CrossRef][Medline]
Bren, A. & Eisenbach, M. (2000). How signals are heard during bacterial chemotaxis: protein-protein interactions in sensory signal propagation. J Bacteriol 182, 68656873.
Bren, A. & Eisenbach, M. (2001). Changing the direction of flagellar rotation in bacteria by modulating the ratio between the rotational states of the switch protein FliM. J Mol Biol 312, 699709.[CrossRef][Medline]
Burgess-Cassler, A. & Ordal, G. W. (1982). Functional homology of Bacillus subtilis methyltransferase II and Escherichia coli CheR protein. J Biol Chem 257, 1283512838.
Burgess-Cassler, A., Ullah, A. H. & Ordal, G. W. (1982). Purification and characterization of Bacillus subtilis methyl-accepting chemotaxis protein methyltransferase II. J Biol Chem 257, 84128417.
Cercignani, G., Lucia, S. & Petracchi, D. (1998). Photoresponses of Halobacterium salinarum to repetitive pulse stimuli. Biophys J 75, 14661472.
Falke, J. J. & Hazelbauer, G. L. (2001). Transmembrane signaling in bacterial chemoreceptors. Trends Biochem Sci 26, 257265.[CrossRef][Medline]
Falke, J. J. & Kim, S. H. (2000). Structure of a conserved receptor domain that regulates kinase activity: the cytoplasmic domain of bacterial taxis receptors. Curr Opin Struct Biol 10, 462469.[CrossRef][Medline]
Fosnaugh, K. & Greenberg, E. P. (1988). Motility and chemotaxis of Spirochaeta aurantia: computer-assisted motion analysis. J Bacteriol 170, 17681774.[Medline]
Fredrick, K. L. & Helmann, J. D. (1994). Dual chemotaxis signaling pathways in Bacillus subtilis: a sigma D-dependent gene encodes a novel protein with both CheW and CheY homologous domains. J Bacteriol 176, 27272735.[Abstract]
Fuhrer, D. K. & Ordal, G. W. (1991). Bacillus subtilis CheN, a homolog of CheA, the central regulator of chemotaxis in Escherichia coli. J Bacteriol 173, 74437448.[Medline]
Garrity, L. F. & Ordal, G. W. (1997). Activation of the CheA kinase by asparagine in Bacillus subtilis chemotaxis. Microbiology 143, 29452951.[Medline]
Goldman, D. J., Nettleton, D. O. & Ordal, G. W. (1984). Purification and characterization of chemotactic methylesterase from Bacillus subtilis. Biochemistry 23, 675680.[Medline]
Hanlon, D. W. & Ordal, G. W. (1994). Cloning and characterization of genes encoding methyl-accepting chemotaxis proteins in Bacillus subtilis. J Biol Chem 269, 1403814046.
Hanlon, D. W., Marquez-Magana, L. M., Carpenter, P. B., Chamberlin, M. J. & Ordal, G. W. (1992). Sequence and characterization of Bacillus subtilis CheW. J Biol Chem 267, 1205512060.
Hanlon, D. W., Ying, C. & Ordal, G. W. (1993). Purification and reconstitution of the methyl-accepting chemotaxis proteins from Bacillus subtilis. Biochim Biophys Acta 1158, 345351.[Medline]
Hess, J. F., Bourret, R. B. & Simon, M. I. (1988a). Histidine phosphorylation and phosphoryl group transfer in bacterial chemotaxis. Nature 336, 139143.[CrossRef][Medline]
Hess, J. F., Oosawa, K., Kaplan, N. & Simon, M. I. (1988b). Phosphorylation of three proteins in the signaling pathway of bacterial chemotaxis. Cell 53, 7987.[Medline]
Karatan, E., Saulmon, M. M., Bunn, M. W. & Ordal, G. W. (2001). Phosphorylation of the response regulator CheV is required for adaptation to attractants during Bacillus subtilis chemotaxis. J Biol Chem 276, 4361843626.
Kirby, J. R., Kristich, C. J., Feinberg, S. L. & Ordal, G. W. (1997). Methanol production during chemotaxis to amino acids in Bacillus subtilis. Mol Microbiol 24, 869878.[CrossRef][Medline]
Kirby, J. R., Saulmon, M. M., Kristich, C. J. & Ordal, G. W. (1999). CheY-dependent methylation of the asparagine receptor, McpB, during chemotaxis in Bacillus subtilis. J Biol Chem 274, 1109211100.
Kirby, J. R., Niewold, T. B., Maloy, S. & Ordal, G. W. (2000). CheB is required for behavioural responses to negative stimuli during chemotaxis in Bacillus subtilis. Mol Microbiol 35, 4457.[CrossRef][Medline]
Kirby, J. R., Kristich, C. J., Saulmon, M. M., Zimmer, M. A., Garrity, L. F., Zhulin, I. B. & Ordal, G. W. (2001). CheC is related to the family of flagellar switch proteins and acts independently from CheD to control chemotaxis in Bacillus subtilis. Mol Microbiol 42, 573585.[CrossRef][Medline]
Kirsch, M. L., Peters, P. D., Hanlon, D. W., Kirby, J. R. & Ordal, G. W. (1993a). Chemotactic methylesterase promotes adaptation to high concentrations of attractant in Bacillus subtilis. J Biol Chem 268, 1861018616.
Kirsch, M. L., Zuberi, A. R., Henner, D., Peters, P. D., Yazdi, M. A. & Ordal, G. W. (1993b). Chemotactic methyltransferase promotes adaptation to repellents in Bacillus subtilis. J Biol Chem 268, 2535025356.
Kristich, C. J. & Ordal, G. W. (2002). Bacillus subtilis CheD is a chemoreceptor modification enzyme required for chemotaxis. J Biol Chem 277, 2535625362.
Lukat, G. S. & Stock, J. B. (1993). Response regulation in bacterial chemotaxis. J Cell Biochem 51, 4146.[Medline]
Macnab, R. M. & Koshland, D. E., Jr (1972). The gradient-sensing mechanism in bacterial chemotaxis. Proc Natl Acad Sci U S A 69, 25092512.[Abstract]
Morrison, T. B. & Parkinson, J. S. (1997). A fragment liberated from the Escherichia coli CheA kinase that blocks stimulatory, but not inhibitory, chemoreceptor signaling. J Bacteriol 179, 55435550.[Abstract]
Nordmann, B., Lebert, M. R., Alam, M., Nitz, S., Kollmannsberger, H., Oesterhelt, D. & Hazelbauer, G. L. (1994). Identification of volatile forms of methyl groups released by Halobacterium salinarium. J Biol Chem 269, 1644916454.
Ordal, G. W., Villani, D. P. & Gibson, K. J. (1977). Amino acid chemoreceptors of Bacillus subtilis. J Bacteriol 129, 156165.[Medline]
Ordal, G. W., Nettleton, D. O. & Hoch, J. A. (1983). Genetics of Bacillus subtilis chemotaxis: isolation and mapping of mutations and cloning of chemotaxis genes. J Bacteriol 154, 10881097.[Medline]
Rosario, M. M. & Ordal, G. W. (1996). CheC and CheD interact to regulate methylation of Bacillus subtilis methyl-accepting chemotaxis proteins. Mol Microbiol 21, 511518.[Medline]
Rosario, M. M., Fredrick, K. L., Ordal, G. W. & Helmann, J. D. (1994). Chemotaxis in Bacillus subtilis requires either of two functionally redundant CheW homologs. J Bacteriol 176, 27362739.[Abstract]
Rosario, M. M., Kirby, J. R., Bochar, D. A. & Ordal, G. W. (1995). Chemotactic methylation and behavior in Bacillus subtilis: role of two unique proteins, CheC and CheD. Biochemistry 34, 38233831.[Medline]
Rudolph, J. & Oesterhelt, D. (1996). Deletion analysis of the che operon in the archaeon Halobacterium salinarium. J Mol Biol 258, 548554.[CrossRef][Medline]
Scharf, B. E., Fahrner, K. A., Turner, L. & Berg, H. C. (1998). Control of direction of flagellar rotation in bacterial chemotaxis. Proc Natl Acad Sci U S A 95, 201206.
Slack, F. J., Serror, P., Joyce, E. & Sonenshein, A. L. (1995). A gene required for nutritional repression of the Bacillus subtilis dipeptide permease operon. Mol Microbiol 15, 689702.[Medline]
Sourjik, V. & Berg, H. C. (2002). Binding of the Escherichia coli response regulator CheY to its target measured in vivo by fluorescence resonance energy transfer. Proc Natl Acad Sci U S A 99, 1266912774.
Springer, W. R. & Koshland, D. E., Jr (1977). Identification of a protein methyltransferase as the cheR gene product in the bacterial sensing system. Proc Natl Acad Sci U S A 74, 533537.[Abstract]
Spudich, E. N., Takahashi, T. & Spudich, J. L. (1989). Sensory rhodopsins I and II modulate a methylation/demethylation system in Halobacterium halobium phototaxis. Proc Natl Acad Sci U S A 86, 77467750.[Abstract]
Stock, J. & Levit, M. (2000). Signal transduction: hair brains in bacterial chemotaxis. Curr Biol 10, R1114.[CrossRef][Medline]
Stock, J. B. & Koshland, D. E., Jr (1978). A protein methylesterase involved in bacterial sensing. Proc Natl Acad Sci U S A 75, 36593663.[Abstract]
Szurmant, H., Bunn, M. W., Cannistraro, V. J. & Ordal, G. W. (2003). Bacillus subtilis hydrolyzes CheY-P at the location of its action, the flagellar switch. J Biol Chem 278, 4861148616.
Taylor, B. L., Zhulin, I. B. & Johnson, M. S. (1999). Aerotaxis and other energy-sensing behavior in bacteria. Annu Rev Microbiol 53, 103128.[CrossRef][Medline]
Terwilliger, T. C., Wang, J. Y. & Koshland, D. E., Jr (1986). Kinetics of receptor modification. The multiply methylated aspartate receptors involved in bacterial chemotaxis. J Biol Chem 261, 1081410820.
Toker, A. S. & Macnab, R. M. (1997). Distinct regions of bacterial flagellar switch protein FliM interact with FliG, FliN and CheY. J Mol Biol 273, 623634.[CrossRef][Medline]
Toker, A. S., Kihara, M. & Macnab, R. M. (1996). Deletion analysis of the FliM flagellar switch protein of Salmonella typhimurium. J Bacteriol 178, 70697079.[Abstract]
Ullah, A. H. & Ordal, G. W. (1981). Purification and characterization of methyl-accepting chemotaxis protein methyltransferase I in Bacillus subtilis. Biochem J 199, 795805.[Medline]
Zhao, R., Collins, E. J., Bourret, R. B. & Silversmith, R. E. (2002). Structure and catalytic mechanism of the E. coli chemotaxis phosphatase CheZ. Nat Struct Biol 9, 570575.[Medline]
Zimmer, M. A., Tiu, J., Collins, M. A. & Ordal, G. W. (2000). Selective methylation changes on the Bacillus subtilis chemotaxis receptor McpB promote adaptation. J Biol Chem 275, 2426424272.
Zimmer, M. A., Szurmant, H., Saulmon, M. M., Collins, M. A., Bant, J. S. & Ordal, G. W. (2002). The role of heterologous receptors in McpB-mediated signalling in Bacillus subtilis chemotaxis. Mol Microbiol 45, 555568.[CrossRef][Medline]
Received 6 May 2003;
revised 25 September 2003;
accepted 7 November 2003.