Bacillus subtilis mutant LicT antiterminators exhibiting enzyme I- and HPr-independent antitermination affect catabolite repression of the bglPH operon.
The Bacillus subtilis antiterminator LicT regulates the expression of bglPH and bglS, which encode the enzymes for the metabolism of aryl-beta-glucosides and the beta-glucanase BglS. The N-terminal domain of LicT (first 55 amino acids) prevents the formation of rho-independent terminators on the respective transcripts by binding to target sites overlapping these terminators. Proteins of the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) regulate the antitermination activity of LicT by phosphorylating histidines in its two PTS regulation domains (PRDs). Phosphorylation at His-100 in PRD-1 requires the PTS proteins enzyme I and HPr and the phosphorylated permease BglP and inactivates LicT. During transport and phosphorylation of aryl-beta-glucosides, BglP is dephosphorylated, which renders LicT active and thus leads to bglPH and bglS induction. In contrast, phosphorylation at His-207 and/or His-269 in PRD-2, which requires only enzyme I and HPr, is absolutely necessary for LicT activity and bglPH and bglS expression. We isolated spontaneous licT mutants expressing bglPH even when enzyme I and HPr were absent (as indicated by the designation "Pia" [PTS-independent antitermination]). Introduced in a ptsHI(+) strain, two classes of licT(Pia) mutations could be distinguished. Mutants synthesizing LicT(Pia) antiterminators altered in PRD-2 still required induction by aryl-beta-glucosides, whereas mutations affecting PRD-1 caused constitutive bglPH expression. One of the two carbon catabolite repression (CCR) mechanisms operative for bglPH requires the rho-independent terminator and is probably prevented when LicT is activated by P approximately His-HPr-dependent phosphorylation in PRD-2 (where the prefix "P approximately " stands for "phospho"). During CCR, the small amount of P approximately His-HPr present in cells growing on repressing PTS sugars probably leads to insufficient phosphorylation at PRD-2 of LicT and therefore to reduced bglPH expression. In agreement with this concept, mutants synthesizing a P approximately His-HPr-independent LicT(Pia) had lost LicT-modulated CCR.
Lindner
Cordula
C
Laboratoire de Génétique des Microorganismes, INRA-CNRS, URA1925, F-78850 Thiverval-Grignon, France.
Hecker
Michael
M
Le Coq
Dominique
D
Deutscher
Josef
J
D001412:Bacillus subtilis / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000502:physiology*; D005959:Glucosidases / Q000235:genetics*; D009154:Mutation; D009876:Operon; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000235:genetics* / Q000502:physiology*; D017852:Phosphotransferases (Nitrogenous Group Acceptor) / Q000502:physiology*; D014157:Transcription Factors / Q000737:chemistry / Q000502:physiology*
D001426:Bacterial Proteins; C098955:LicT protein, Bacteria; D014157:Transcription Factors; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C030182:phosphocarrier protein HPr; C031629:phosphoenolpyruvate-glucose phosphotransferase; D017852:Phosphotransferases (Nitrogenous Group Acceptor); C022360:phosphoenolpyruvate-protein phosphotransferase; D005959:Glucosidases; C066586:6-phospho-beta-glucosidase