Michael Hecker,2 Dominique Le Coq,1 and Josef Deutscher1*
Laboratoire de Génétique des Microorganismes, INRA-CNRS, URA1925, F-78850 Thiverval-Grignon, France,1 Institut für Mikrobiologie und Molekularbiologie, Ernst-Moritz-Arndt-Universität, D-17487 Greifswald, Germany2
Received 18 March 2002/ Accepted 4 June 2002
The Bacillus subtilis antiterminator LicT regulates the expression of bglPH and bglS, which encode the enzymes for the metabolism of aryl-ß-glucosides and the ß-glucanase BglS. The N-terminal domain of LicT (first 55 amino acids) prevents the formation of
-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-ß-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-ß-glucosides, whereas mutations affecting PRD-1 caused constitutive bglPH expression. One of the two carbon catabolite repression (CCR) mechanisms operative for bglPH requires the
-independent terminator and is probably prevented when LicT is activated by P
His-HPr-dependent phosphorylation in PRD-2 (where the prefix "P
" stands for "phospho"). During CCR, the small amount of P
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
His-HPr-independent LicT(Pia) had lost LicT-modulated CCR.
Present address: Friesland Coberco Dairy Foods Corporate Research, 7418 BA Deventer, The Netherlands
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