Affiliation:
1. Microbial Ingredients Section, NIZO Food Research, 6710 BA Ede, The Netherlands
Abstract
ABSTRACT
The
Lactococcus lactis ptsH
and
ptsI
genes, encoding the general proteins of the phosphoenolpyruvate-dependent phosphotransferase system, HPr and enzyme I, respectively, were cloned, and the regulatory role of HPr was studied by mutational analysis of its gene. A promoter sequence was identified upstream of the
ptsHI
operon, and the transcription start site was mapped by primer extension. The results of Northern analyses showed the presence of two glucose-inducible transcripts, one of 0.3 kb containing
ptsH
and a second of 2.0 kb containing both
ptsH
and
ptsI
. Disruption of the
ptsH
and
ptsI
genes in strain NZ9800 resulted in a reduced growth rate at the expense of glucose, but no growth at the expense of sucrose and fructose, confirming the dominant role of the phosphotransferase system in the uptake of these sugars in
L. lactis
. Complementation of the
ptsH
and
ptsI
mutants with the intact genes under the control of a regulated promoter resulted in the restoration of the wild-type phenotype. The role of HPr(Ser-P) in the recently established CcpA-mediated control of galactose metabolism as well as glycolysis was analyzed by producing an HPr mutant carrying an aspartic acid on residue 46 which mimicks a phosphorylated serine. The results of these experiments demonstrated the role of HPr(Ser-P) as corepressor in the catabolite repression of the
gal
operon. Furthermore, we show for the first time that HPr(Ser-P) functions as a coactivator in the CcpA-mediated catabolite activation of the pyruvate kinase and
l
-lactate dehydrogenase genes.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
52 articles.
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