Products of the pts operon of Escherichia coil have multiple physiological
roles such as sugar transport, and the operon is controlled by two promoter
s, PO and P1, Expression of the pts PO promoter that is increased during gr
owth in the presence of glucose is also activated by cAMP receptor protein
cAMP. Based on the existence of a sequence that has a high similarity with
the known Rile binding site in the promoter, the effects of the Mlc protein
on the pts PO promoter expression were studied. In vivo transcription assa
ys using wild type and mlc-negative E. coil strains grown in the presence a
nd absence of glucose indicate that Mlc negatively regulates expression of
the PO promoter, and Mlc-dependent repression is relieved by glucose in the
growth medium. In vitro transcription assay using purified recombinant Mlc
showed that Mlc repressed transcription from the PO but did not affect the
activity of the P1, DNase I footprinting experiments revealed that a Rile
binding site was located around +1 to +25 of the pro meter and that Mlc inh
ibited the binding of RNA polymerase to the PO promoter. Cells overexpressi
ng Mlc showed a very slow fermentation rate compared with the wild type whe
n grown in the presence of various phosphoenolpyruvate-carbohydrate phospho
transferase system sugars but few differences in the presence of non-phosph
oenolpyruvate-carbohydrate phosphotransferase system sugars except maltose,
These results suggest that the pts operon is one of major targets for the
negative regulation by Mlc, and thus Mle regulates the utilization of vario
us sugars as well as glucose in E. coil, The possibility that the inducer o
f Mlc may not be sugar or its derivative but an unknown factor is proposed
to explain the Mlc induction mechanism by various sugars.