J. Green et al., REGULATION OF THE NDH GENE OF ESCHERICHIA-COLI BY INTEGRATION HOST FACTOR AND A NOVEL REGULATOR, ARR, Microbiology, 143, 1997, pp. 2865-2875
The ndh gene of Escherichia coil encodes the non-proton-translocating
NADH dehydrogenase II. Expression of the ndh gene is subject to a comp
lex network of regulatory controls at the transcriptional level. Under
anaerobic conditions ndh is repressed by the regulator of fumarate an
d nitrate reduction (FNR). However, in the absence of FNR, ndh express
ion is activated by the amino acid response regulator (Arr) during ana
erobic growth in rich medium. Expression of the ndh gene varies during
the growth cycle in response to the intracellular concentration of th
e heat-stable DNA-binding protein, Fis. In this work two additional he
at-stable proteins, integration host factor (IHF) and the histonelike
protein HU were found to interact with the ndh promoter. IHF was shown
to bind at three sites centred at +26, -17 and -58 in the ndh promote
r (K-d = 10(-8) M), to prevent open-complex formation and to repress n
dh transcription in vitro. Studies with an ndh-lacZ fusion confirmed t
hat IHF represses ndh expression in vivo. Two putative binding sites f
or Arr, which overlap the two FNR boxes in the ndh promoter, were iden
tified. Studies with the FNR-activated and amino-acid-inducible aspara
ginase II gene (ansB) showed that IHF and a component of the Arr-conta
ining fraction (but not HU) interact with the corresponding ansB promo
ter.