Journal of Bacteriology, June 2001, p. 3391-3398, Vol. 183, No. 11
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.11.3391-3398.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


Laboratoire de Génétique des Microorganismes, INRA-CNRS URA 1925, 78850 Thiverval-Grignon,1 and Génétique Microbienne, INRA, 78352 Jouy en Josas, France,3 and NIZO Food Research, 6710 BA Ede, The Netherlands2
Received 18 December 2000/Accepted 19 March 2001
In most low-G+C gram-positive bacteria, the phosphoryl carrier
protein HPr of the phosphoenolpyruvate:sugar phosphotransferase system
(PTS) becomes phosphorylated at Ser-46. This ATP-dependent reaction is
catalyzed by the bifunctional HPr kinase/P-Ser-HPr phosphatase. We
found that serine-phosphorylated HPr (P-Ser-HPr) of Lactococcus
lactis participates not only in carbon catabolite repression of
an operon encoding a
-glucoside-specific EII and a
6-P-
-glucosidase but also in inducer exclusion of the non-PTS carbohydrates maltose and ribose. In a wild-type strain, transport of
these non-PTS carbohydrates is strongly inhibited by the presence of
glucose, whereas in a ptsH1 mutant, in which Ser-46 of HPr is replaced with an alanine, glucose had lost its inhibitory effect. In
vitro experiments carried out with L. lactis vesicles had
suggested that P-Ser-HPr is also implicated in inducer expulsion of
nonmetabolizable homologues of PTS sugars, such as methyl
-D-thiogalactoside (TMG) and
2-deoxy-D-glucose (2-DG). In vivo experiments with the
ptsH1 mutant established that P-Ser-HPr is not necessary
for inducer expulsion. Glucose-activated 2-DG expulsion occurred at
similar rates in wild-type and ptsH1 mutant strains,
whereas TMG expulsion was slowed in the ptsH1 mutant. It
therefore seems that P-Ser-HPr is not essential for inducer expulsion
but that in certain cases it can play an indirect role in this
regulatory process.
Present address: Departamento de Biotecnologia, Instituto de
Agroquímica y Tecnología de Alimentos (CSIC), Valencia, Spain.
Present address: Department of Genetics, University of Groningen,
9751 NN Haren, The Netherlands.
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