Antitermination by GlpP, catabolite repression via CcpA and inducer exclusion triggered by P-GlpK dephosphorylation control Bacillus subtilis glpFK expression.
The Bacillus subtilis glpFK operon encoding the glycerol transport facilitator (GlpF) and glycerol kinase (GlpK) is induced by glycerol-3-P and repressed by rapidly metabolizable sugars. Carbon catabolite repression (CCR) of glpFK is partly mediated via a catabolite response element cre preceding glpFK. This operator site is recognized by the catabolite control protein A (CcpA) in complex with one of its co-repressors, P-Ser-HPr or P-Ser-Crh. HPr is a component of the phosphoenolpyruvate:sugar phosphotransferase system (PTS), and Crh is an HPr homologue. The hprK-encoded HPr kinase phosphorylates HPr and Crh at Ser-46. But in neither ccpA nor hprK mutants was expression of a glpF'-lacZ fusion relieved from CCR, as a second, CcpA-independent CCR mechanism implying the terminator tglpFK, whose formation is prevented by the glycerol-3-P-activated antiterminator GlpP, is operative. Deletion of tglpFK led to elevated expression of the glpF'-lacZ fusion and to partial relief from CCR. CCR completely disappeared in DeltatglpFK mutants carrying a disruption of ccpA or hprK. The tglpFK-requiring CCR mechanism seems to be based on insufficient synthesis of glycerol-3-P, as CCR of glpFK was absent in ccpA mutants growing on glycerol-3-P or synthesizing H230R mutant GlpK. In cells growing on glycerol, glucose prevents the phosphorylation of GlpK by P-His-HPr. P-GlpK is much more active than GlpK, and the absence of P~GlpK formation in DeltaptsHI strains prevents glycerol metabolism. As a consequence, only small amounts of glycerol-3-P will be formed in glycerol and glucose-exposed cells (inducer exclusion). The uptake of glycerol-3-P via GlpT provides high concentrations of this metabolite in the ccpA mutant and allows the expression of the glpF'-lacZ fusion even when glucose is present. Similarly, despite the presence of glucose, large amounts of glycerol-3-P are formed in a glycerol-exposed strain synthesizing GlpKH230R, as this mutant GlpK is as active as P-GlpK.
Darbon
Emmanuelle
E
Laboratoire de Génétique des Microorganismes, INRA-CNRS, URA1925, F-78850 Thiverval-Grignon, France.
Servant
Pascale
P
Poncet
Sandrine
S
Deutscher
Josef
J
D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D005991:Glycerol Kinase / Q000235:genetics*; D005994:Glycerophosphates / Q000378:metabolism; D006639:Histidine / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009876:Operon; D010728:Phosphoenolpyruvate / Q000378:metabolism; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000378:metabolism; D010766:Phosphorylation; D011993:Recombinant Fusion Proteins / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D005994:Glycerophosphates; D026901:Membrane Transport Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C069286:catabolite control proteins, bacteria; C079802:glpP protein, Bacillus subtilis; D006639:Histidine; D010728:Phosphoenolpyruvate; C029620:alpha-glycerophosphoric acid; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C030182:phosphocarrier protein HPr; D005991:Glycerol Kinase