Department of Biological and Chemical Sciences, The University of the West Indies, Cave Hill Campus, Barbados1
Author for correspondence: Sarah L. Sutrina. Tel: +1 246 417 4360. Fax: +1 246 417 4325. e-mail: ssutrina{at}uwichill.edu.bb
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ABSTRACT |
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Keywords: phosphoenolpyruvate:sugar phosphotransferase system, carbon catabolite control, gene regulation, carbohydrate transport
Abbreviations: CAP, catabolite activator protein; DTP, diphosphoryltransfer protein; EI/EII, enzymes I/II; Fru, fructose; Glc, glucose; GlcNAc, N-acetylglucosamine; Gut, glucitol; Mtl, mannitol; PEP, phosphoenolpyruvate; PTS, phosphotransferase system
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INTRODUCTION |
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The fructose PTS is structurally unique in that its HPr counterpart is a domain of a larger protein, DTP (diphosphoryltransfer protein); the other two domains are the sugar-specific phosphocarrier domain EIIAFru and a third domain M (modulator) which is thought to play a regulatory role (Geerse et al., 1989 ; Wu et al., 1990
). It has been long established that FPr can substitute for HPr in PTSs for other sugars besides fructose both in vivo and in vitro (Saier et al., 1970
, 1976
). In complementation assays it was observed that purified FPr, whether as part of the larger DTP or in the form of a 9 kDa separate protein (free FPr), worked about 5% as well as HPr in the PTSs for mannose, N-acetylglucosamine, mannitol and glucitol, but only 0·5% as well as HPr in the glucose-specific PTS (Sutrina et al., 1988
). More recently, in vitro assays by a different group indicated that both DTP and free FPr accepted a phosphate group from EI about 40% as well as HPr, and donated the phosphate group to EIIAMtl about as well as HPr (Lux et al., 1995
). These results taken together suggest that FPr, molecule for molecule, does not interact with EI as effectively as HPr, and that it also interacts relatively poorly with the A domain of the glucose-specific Enzyme II (EIIAGlc) compared to other EIIAs. In a recent study, DTP was also shown to substitute for HPr in both the activation of the antiterminator BglG of the ß-glucosides (bgl) operon of E. coli and in the negative regulation of this same protein by phospho-Enzyme IIBCABgl (Görke & Rak, 1999
).
In E. coli and S. typhimurium, EIIAGlc mediates control of utilization of non-PTS sugars by the PTS (reviewed by Saier, 1989 ; Postma et al., 1993
; Meadow et al., 1990
). A model to account for this was proposed. When in its phosphorylated form, EIIAGlc-P activates adenylate cyclase (Reddy & Kamireddi, 1998
). When in its unphosphorylated form, EIIAGlc prevents the uptake of non-PTS sugars by binding to and inhibiting the permeases for these sugars, or, in the case of glycerol, by binding to and inhibiting glycerol kinase, a phenomenon called inducer exclusion. In the absence of PTS sugars, the ratio of EIIAGlc-P to EIIAGlc is relatively high, leading to relatively high levels of cAMP and to active non-PTS permeases. This allows for high level expression of catabolite activator protein (CAP)cAMP-activated operons in general and to induction of the genes for the uptake and utilization of the non-PTS sugars in particular. In the presence of a PTS sugar, phosphate is drained off EIIAGlc-P, and inducer exclusion/catabolite repression results. Recent studies challenge the model just described; it has been proposed, based on these studies, that the role of cAMP in glucose/lactose diauxie in E. coli is to enhance inducer exclusion by activating the membrane component of the glucose PTS, EIICBGlc, at the transcriptional level (Inada et al., 1996
; Kimata et al., 1997
). In contrast, another recent study suggests that, in E. coli, cAMP-dependent catabolite repression, rather than inducer exclusion, may be the dominant mechanism by which glucose represses glycerol kinase levels during diauxic growth (Holtman et al., 2001
). In S. typhimurium, both mechanisms may be important in glucose/glycerol diauxie (Novotny et al., 1985
).
In S. typhimurium strain LJ705 the structural genes for EI and HPr have been deleted, and the fruR gene encoding the fructose repressor protein FruR, or Cra, has been disrupted by a Tn10 insertion; this strain also expresses the normally cryptic EI-like protein EIFru (EI*), which is part of the fru regulon (Chin et al., 1987 ). This strain is able to grow on PTS sugars, since the constitutively expressed FPr (DTP) and EIFru substitute for the missing HPr and EI. In this study, we found that growth of LJ705 on the PTS sugar glucitol as its sole carbon source is poor to negligible and that its growth on the non-PTS sugars melibiose, maltose and especially glycerol is also poor. Addition of cAMP to the growth medium markedly improved growth on glucitol, but not on glycerol. We propose that underphosphorylation of EIIAGlc by FPr in this strain is responsible for these effects; low cAMP leads to low activation of the CAPcAMP-dependent glucitol operon (Yamada & Saier, 1988
) and a high EIIAGlc/EIIAGlc-P ratio causes inducer exclusion of non-PTS sugars even in the absence of PTS sugars. In this study we have focussed primarily on the lack of ability of LJ705 to grow on glucitol. Its poor growth on non-PTS sugars is currently under further investigation.
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METHODS |
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Strains.
Salmonella typhimurium strains used were LJ705 (cysK ptsHI41 fruR51::Tn10 ptsJ52), SB1475 (ptsH15), SB3507 (trpB223), SB1667 (mal) and SB1744 (mtlA61). The ptsJ52 mutation in LJ705 allows expression of the normally cryptic EIFru. All of these strains are derivatives of wild-type strain LT-2. Escherichia coli strains used were K12 (wild-type) and ESK147 (F- ompT rß- mß- plysS cmr). Strains ESK147 (E. B. Waygood, Department of Biochemistry, University of Saskatchewan), SB3507 (Cordaro & Roseman, 1972
) and SB1667 (M. H. Saier, Jr, University of California at San Diego) are wild-type with respect to the PTS.
Preparation of crude extracts.
Cultures were grown to late exponential phase in LB broth and harvested by centrifugation. The pellets were washed twice with 0·15 M NaCl and once with buffer (50 mM Tris/HCl, pH 7·5, 1 mM EDTA, 0·1 mM PMSF, 0·2 mM DTT), then resuspended in a small volume of the same buffer. The suspensions were passed through the French press three times at 10000 p.s.i. (69 MPa). Unbroken cells and debris were removed by centrifugation (10000 r.p.m., 10 min, JA17 rotor).
Preparation of washed membranes.
Crude extracts were subjected to centrifugation for 4 h at 15000 r.p.m. in a JA17 rotor. The membrane pellets were resuspended in the above buffer and the centrifugation step was repeated. The washed membrane pellets were resuspended in a minimal volume of buffer.
Assays.
Complementation assays for PTS components were conducted as previously described, using 14C-labelled sugar substrates and PEP (Reizer et al., 1992 ). In assays of crude extracts for the sugar-specific PTS components, partially purified HPr and EI were added to ensure an excess of these general energy-coupling proteins.
Transphosphorylation assays for the glucitol-specific membrane component EII(BC)Gut were conducted as previously described (Saier et al., 1977 ). Assay mixtures contained 10 µM [14C]glucitol [5 µCi µmol-1 (1·85 kBq µmol-1)] as substrate and 10 mM glucitol 6-phosphate as phosphate donor as well as 50 mM KPO4, pH 6·0, 25 mM KF, 12·5 mM MgCl2, 2·5 mM DTT and the membrane preparation being assayed; the total volume was 100 µl. After incubation for 30 min at 37 °C, the reactions were stopped by adding 1 ml water. The [14C]glucitol phosphate product was collected using anion exchange columns and quantified with a scintillation counter (Kundig & Roseman, 1971
). The Lowry assay was used to determine total protein concentration.
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RESULTS AND DISCUSSION |
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On minimal medium, growth of LJ705 was poor to negligible, with respect to both rate and extent, on the PTS sugar glucitol relative to its growth on other PTS sugars (glucose, fructose, N-acetylglucosamine, mannose and mannitol) or galactose. Growth on mannitol was also somewhat slow compared to the other PTS sugars, and growth on glucose (and galactose, which is not shown) somewhat fast (Fig. 1b). The growth rate did not increase when the concentration of glucitol was increased from the 0·2% used in most of our studies to 0·5% or 1%; decreasing the concentration also did not promote growth. This strain also grew very poorly on the non-PTS sugars maltose, melibiose and especially glycerol (not shown). We normally included tetracycline (20 µg ml-1) in the medium for LJ705; omission of the drug did not affect the growth rate.
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On rich medium, little difference in growth rate or extent was observed when LJ705 was grown on unsupplemented LB or on glucose, fructose, mannitol or glucitol or combinations of glucitol and one of the other sugars, and there was no large difference between growth rates of LJ705 and the wild-type strain SB3507. Supplementing minimal medium with tryptone (0·5%) also minimized the differences in growth rate. On fermentation plates, glucitol effects were subtle; LJ705 generally showed a slightly slower positive response on EMB or MacConkey plates containing glucitol than did wild-type strains. This was not reported previously. All strains tested showed a weak response on glucitol plates relative to other PTS sugars.
Since glucitol did not hinder growth of LJ705 on rich medium or on medium supplemented with other sugars, the effect did not appear to be due to toxicity due, for example, to build-up of glucitol 6-phosphate as a result of defective glucitol-6-phosphate dehydrogenase. Rather, the strain seemed to be unable to utilize glucitol as a growth substrate.
Growth of a ptsH mutant versus LJ705
One possible explanation for the inability of LJ705 to grow on glucitol is that FPr interacts so poorly with the glucitol-specific PTS protein EIIAGut that glucitol cannot be taken up fast enough to support growth. This seemed unlikely since a previous in vitro study indicated that FPr substitutes equally well for HPr in the PTSs for mannitol, mannose, glucitol and N-acetylglucosamine, and relatively (10x) poorly only in the glucose system (Sutrina et al., 1988 ). On the other hand, the in vitro study was done under conditions such that cross-reactivity between the glucitol and mannitol systems could have confused the results (Saier et al., 1977
). To investigate this possibility, we compared growth of LJ705 to that of S. typhimurium strain SB1475 (Saier et al., 1976
), which carries a point mutation in the structural gene for HPr, ptsH. The latter strain has negligible HPr activity, and because the ptsH mutation is pleiotropic, it also has low EI activity; in contrast to LJ705, it does not express EIFru and production of FPr (DTP) is not constitutive.
As expected, SB1475 grew relatively well (usually slightly more slowly than LJ705) on fructose, but not on most other PTS sugars, as the sole carbon source; it grew, slowly, on glucose (Fig. 1c). As expected, on minimal medium supplemented with a mixture of fructose (0·02%) and glucitol, mannitol, mannose or N-acetylglucosamine (0·2%), this strain continued to grow on the other PTS sugar after the fructose should have been consumed (or grew on both sugars simultaneously), using fructose-induced FPr to substitute for HPr in the uptake of the other PTS sugars (Fig. 1d
). Thus, poor interaction of FPr with the glucitol PTS cannot be the sole explanation for the failure of LJ705 to grow on glucitol. Interestingly, glucitol and mannitol seemed to slow down growth of SB1475 on fructose, N-acetylglucosamine may have increased the growth rate on fructose slightly, and growth on a mixture of fructose and glucose was monophasic and considerably more rapid than on fructose alone. The latter result was surprising, since FPr works poorly with EIIAGlc, but was consistent with the finding that LJ705 grew better on glucose than on other PTS sugars. The fact that glucose is capable of entering S. typhimurium cells via routes other than the glucose-specific PTS, e.g., it is a good substrate of the mannose PTS and is also a substrate of the non-PTS galactose permease (Postma & Stock, 1980
), probably accounts for these results.
Effect of cAMP on growth of LJ705
Although FPr substitutes for HPr, it interacts relatively poorly with EI (Lux et al., 1995 ; Sutrina et al., 1988
), and, as mentioned above, the latter study suggested that, relative to other EIIAs, its interaction with EIIAGlc is particularly poor. Thus this mediator of inducer exclusion/catabolite repression may be underphosphorylated in LJ705. It is possible that the substitution of EIFru for EI also contributes to this effect; in vitro studies suggested that EIFru behaves very similarly to EI, but these studies were not extensive (Chin et al., 1987
). This protein remains something of a mystery, since it has not been identified as any of the known paralogues of EI in the sequences of E. coli or S. typhimurium. Since the phosphorylated form of EIIAGlc mediates catabolite repression by activating adenylate cyclase, its underphosphorylation, by FPr, in LJ705 could lead to low levels of cAMP, and thus to low levels of expression of cAMP-dependent operons. The gut operon absolutely requires cAMP for expression (Yamada & Saier, 1988
). The non-PTS operons for glycerol, melibiose and maltose utilization are also under CAPcAMP control.
To test our hypothesis, we added 1 mM cAMP to the medium of either LJ705 or the wild-type strain SB3507 growing on 0·2% glucitol. The cAMP had little effect on the growth rate of the wild-type strain (Fig. 2a). The growth rate of LJ705 increased markedly, after a lag; when the experiment was extended further than the one shown in Fig. 2(b)
, the final density of the culture approached that of the wild-type strain. We also added cAMP to cultures of the wild-type strain, LJ705 and the mutant SB1475 growing on a mixture of 0·2% glucitol and 0·02% fructose. The wild-type strain kept growing on glucitol after the fructose should have been exhausted (or grew on both sugars simultaneously; there was no obvious lag phase); cAMP had no effect on the growth rate (Fig. 2a
). After exhaustion of fructose, the growth rate of LJ705 dropped to its usual negligible level; cAMP allowed a continuation of growth on glucitol, after a lag, and a final density approaching that of the wild-type culture (Fig. 2b
). As above, glucitol appeared to slow down the growth of SB1475 on fructose, but growth continued, at a slow rate, after the fructose should have been exhausted. Addition of cAMP did not appear to affect the growth rate of this mutant strongly; in the experiment shown, a slight positive effect was observed (Fig. 2c
), while a duplicate experiment showed a slight negative effect.
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The results suggest that low expression of the gut operon due to low levels of cAMP is responsible for poor growth of LJ705 on glucitol. On glycerol, addition of cAMP should promote catabolite derepression, but a relatively high ratio of unphosphorylated EIIAGlc to EIIAGlc-P may still cause inducer exclusion (EIIAGlc inhibits glycerol kinase). Our results suggest that the gut operon of S. typhimurium requires higher levels of cAMP for full activation than do the man, mtl, glc and nag PTS operons.
Levels of glucitol-specific PTS components in LJ705 versus other strains
To determine the levels of the glucitol-specific PTS components, strains of S. typhimurium were grown in liquid LB broth supplemented with 0·5% glucitol or with 0·5% glucitol plus another PTS sugar (usually 0·5%) and/or cAMP (1 mM, added at 2·5 h); crude extracts were then prepared and assayed as previously described (Reizer et al., 1992 ). The results (not shown) were difficult to interpret due to interference by the mannitol-specific PTS component EIICBAMtl in the glucitol PTS assay (Grenier et al., 1985
; Saier et al., 1977
). To eliminate this problem, washed membranes were prepared and the transphosphorylation assay was carried out using [14C]glucitol as substrate and glucitol 6-phosphate as phosphate donor (Saier et al., 1977
). Results, expressed as pmol [14C]glucitol 6-P formed min-1 (mg membrane protein)-1, are shown in Table 1
. The specific activity of the membrane component of the glucitol PTS, EII(BC)Gut, was consistently lower (by 5070%) in membranes from glucitol-grown LJ705 compared to membranes from glucitol-grown wild-type strain SB3507. Another wild-type strain, SB1667, was also found to have high specific activity relative to LJ705. In the presence of 1 mM cAMP, specific activities of EII(BC)Gut in both SB3507 and LJ705 membranes increased, but the increase was more substantial for the mutant strain; values for the mutant strain grown with cAMP approached those for the wild-type strain grown without. Thus the rather small deficiency could be responsible for the inability of LJ705 to grow on glucitol.
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Other PTS sugars appeared to repress expression of the glucitol PTS in the wild-type strain; interestingly, mannitol repressed most strongly, fructose least, and glucose and N-acetylglucosamine repressed to a similar intermediate extent. Addition of cAMP did not relieve repression by glucose or mannitol. In strain SB1744 (Saier et al., 1976 ), which has a defective mannitol PTS, mannitol did not strongly repress expression of the glucitol PTS. Growth of wild-type strain SB3507 in the presence of PTS sugars other than glucitol generally resulted in a level of the membrane component EII(BC)Gut about twice that of membranes from cells grown on unsupplemented LB, while glucitol induced about 20x. Results were similar for LJ705, although repression by fructose appeared to be stronger than in the wild-type strain. Fructose, normally a Class B, or weakly repressing, PTS sugar, may be a Class A, or strongly repressing, PTS sugar in fruR (cra) strains (Crasnier-Mednansky et al., 1997
).
Repression of the gut operon by mannitol in wild-type S. typhimurium
To investigate these observations, further growth studies were conducted. When wild-type strain SB3507 was grown on a mixture of 0·02% mannitol and 0·2% glucitol, an obvious lag phase was observed between growth on mannitol and resumption of growth on glucitol (Fig. 3). Such a marked lag was not observed in the presence of 0·02% glucose, fructose or N-acetylglucosamine and 0·2% glucitol, and is consistent with strong repression of the glucitol operon in the presence of mannitol, and with early studies reporting diauxic growth of E. coli on mannitol and glucitol (Lengeler & Lin, 1972
).
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Another possible explanation for the failure of LJ705 to grow on glucitol could be that FPr works too poorly with the glucitol-specific PTS proteins to support growth. To investigate this possibility, mutant strain SB1475, which lacks active HPr and has low EI activity but is wild-type with respect to the fructose-specific PTS, i.e., does not express EIFru at all and does not express FPr (DTP) constitutively, was grown on a mixture of fructose and glucitol. This mutant was able to continue growing on the mixture to a density much higher than on fructose alone, suggesting that it must have been able to take up glucitol using FPr. Thus it seems unlikely that poor interaction of FPr with the glucitol PTS is the sole explanation for the poor growth of LJ705 on glucitol.
Membranes from SB1475 contained maximal levels of EII(BC)Gut only when the strain was grown in the presence of both glucitol and fructose. Surprisingly, this maximal level was similar to that of LJ705 rather than to that of the wild-type strains. It should also be noted that SB1475 has been reported to produce levels of cAMP about 50% those of wild-type strains (Feldheim et al., 1990 ). Thus it is not clear why this strain was able to grow on glucitol, apparently using FPr, while LJ705 was not. Addition of cAMP to the medium did not strongly affect growth of SB1475 on a mixture of fructose and glucitol. Possibly relatively poor interaction of FPr and EIIAGut is a contributing factor to the poor growth of LJ705 on glucitol, in addition to low EII(BC)Gut. It has been reported that increasing cAMP may lead to increased levels of fructose PTS proteins even in fruR strains (Crasnier-Mednansky et al., 1997
). Growing LJ705 in the presence of cAMP could thus increase the levels of both FPr and the glucitol PTS components, as well as EIFru, and a combination of these effects may allow growth on glucitol.
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REFERENCES |
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Cordaro, J. C. & Roseman, S. (1972). Deletion mapping of the genes coding for HPr and Enzyme I of the phosphoenolpyruvate:sugar phosphotransferase system in Salmonella typhimurium. J Bacteriol 112, 17-29.[Medline]
Crasnier-Mednansky, M., Park, M. C., Studley, W. K. & Saier, M. H.Jr (1997). Cra-mediated regulation of Escherichia coli adenylate cyclase. Microbiology 143, 785-792.[Abstract]
Feldheim, D. A., Chin, A. M., Nierva, C. T., Feucht, B. U., Cao, Y. W., Xu, Y. F., Sutrina, S. L. & Saier, M. H.Jr (1990). Physiological consequences of the complete loss of phosphoryl-transfer proteins HPr and FPr of the phosphoenolpyruvate:sugar phosphotransferase system and analysis of fructose (fru) operon expression in Salmonella typhimurium. J Bacteriol 172, 5459-5469.[Medline]
Geerse, R. H., Izzo, F. & Postma, P. W. (1989). The PEP:fructose phosphotransferase system in Salmonella typhimurium: FPr combines Enzyme IIIfru and pseudo-HPr activities. Mol Gen Genet 216, 517-525.[Medline]
Görke, B. & Rak, B. (1999). Catabolite control of Escherichia coli regulatory protein BglG activity by antagonistically acting phosphorylations. EMBO J 18, 3370-3379.
Grenier, F. C., Hayward, I., Novotny, M. J., Leonard, J. E. & Saier, M. H.Jr (1985). Identification of the phosphocarrier protein Enzyme IIIglucitol: essential component of the glucitol phosphotransferase system in Salmonella typhimurium. J Bacteriol 161, 1017-1022.[Medline]
Holtman, C. K., Pawlyk, A. C., Meadow, N. D. & Pettigrew, D. W. (2001). Reverse genetics of Escherichia coli glycerol kinase allosteric regulation and glucose control of glycerol utilization in vivo. J Bacteriol 183, 3336-3344.
Inada, T., Kimata, K. & Aiba, H. (1996). Mechanism responsible for glucose-lactose diauxie in Escherichia coli: challenge to the cAMP model. Genes Cells 1, 293-301.
Kimata, K., Takahashi, H., Inada, T., Postma, P. & Aiba, H. (1997). cAMP receptor protein-cAMP plays a crucial role in glucose-lactose diauxie by activating the major glucose transporter gene in Escherichia coli. Proc Natl Acad Sci USA 92, 11583-11587.[Abstract]
Kundig, W. & Roseman, S. (1971). Sugar transport. I. Isolation of a phosphotransferase system from Escherichia coli. J Biol Chem 246, 1393-1406.
Lengeler, J. & Lin, E. C. C. (1972). Reversal of the mannitol-sorbitol diauxie in Escherichia coli. J Bacteriol 112, 840-848.[Medline]
Lux, R., Jahreis, K., Bettenbrock, K., Parkinson, J. S. & Lengeler, J. W. (1995). Coupling the phosphotransferase system and the methyl-accepting chemotaxis protein-dependent chemotaxis signaling pathways of Escherichia coli. Proc Natl Acad Sci USA 92, 11583-11587.[Abstract]
Meadow, N. D., Fox, D. K. & Roseman, S. (1990). The bacterial phosphoenolpyruvate:glycose phosphotransferase system. Annu Rev Biochem 59, 497-452.[Medline]
Novotny, J. M., Frederickson, W. L., Waygood, E. B. & Saier, M. H.Jr (1985). Allosteric regulation of glycerol kinase by enzyme IIIglc of the phosphotransferase system in Escherichia coli and Salmonella typhimurium. J Bacteriol 162, 810-816.[Medline]
Postma, P. W. & Stock, J. B. (1980). Enzymes II of the phosphotransferase system do not catalyze transport in the absence of phosphorylation. J Bacteriol 141, 476-484.[Medline]
Postma, P. W., Lengeler, J. W. & Jacobson, G. R. (1993). Phosphoenolpyruvate:carbohydrate phosphotransferase systems of bacteria. Microbiol Rev 57, 543-594.[Abstract]
Reddy, P. & Kamireddi, M. (1998). Modulation of Escherichia coli adenylyl cyclase activity by catalytic-site mutants of protein IIAGlc of the phosphoenolpyruvate:sugar phosphotransferase system. J Bacteriol 180, 732-737.
Reizer, J., Sutrina, S. L., Wu, L.-F., Deutscher, J., Reddy, P. & Saier, M. H.Jr (1992). Functional interactions between proteins of the phosphoenolpyruvate:sugar phosphotransferase systems of Bacillus subtilis and Escherichia coli. J Biol Chem 267, 9158-9169.
Saier, M. H.Jr (1989). Protein phosphorylation and allosteric control of inducer exclusion and catabolite repression by the bacterial phosphoenolpyruvate:sugar phosphotransferase system. Microbiol Rev 53, 109-120.
Saier, M. H.Jr, Simoni, R. D. & Roseman, S. (1970). The physiological behavior of Enzyme I and heat-stable protein mutants of a bacterial phosphotransferase system. J Biol Chem 245, 5870-5873.
Saier, M. H.Jr, Simoni, R. D. & Roseman, S. (1976). Sugar transport: properties of mutant bacteria defective in proteins of the phosphoenolpyruvate:sugar phosphotransferase system. J Biol Chem 251, 6584-6597.[Abstract]
Saier, M. H.Jr, Feucht, B. U. & Mora, W. K. (1977). Sugar phosphate:sugar transphosphorylation and exchange group translocation catalyzed by the Enzyme II complexes of the bacterial phosphoenolpyruvate:sugar phosphotransferase system. J Biol Chem 252, 8899-8907.[Medline]
Sutrina, S. L., Chin, A. M., Esch, F. & Saier, M. H.Jr (1988). Purification and characterization of the fructose-inducible HPr-like protein, FPr, and the fructose-specific Enzyme III of the phosphoenolpyruvate:sugar phosphotransferase system of Salmonella typhimurium. J Biol Chem 263, 5061-5069.
Wu, L.-F., Tomich, J. M. & Saier, M. H.Jr (1990). Structure and evolution of a multidomain multiphosphoryl transfer protein. J Mol Biol 213, 687-703.[Medline]
Yamada, M. & Saier, M. H.Jr (1988). Positive and negative regulators for glucitol (gut) operon expression in Escherichia coli. J Mol Biol 203, 569-583.[Medline]
Received 15 April 2002;
revised 23 August 2002;
accepted 30 August 2002.
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