Previously, we have shown that expression of the Escherichia coli aroP P2 p
romoter is partially repressed by the TyrR protein alone and strongly repre
ssed by the TyrR protein in the presence of the coeffector tyrosine or phen
ylalanine (P. Wang, J. Yang, and A. J. Pittard, J. Bacteriol. 179:4206-4212
, 1997). Here we present in vitro results showing that the TyrR protein and
RNA polymerase can bind simultaneously to the aroP P2 promoter. In the pre
sence of tyrosine, the TyrR protein inhibits open complex formation at the
P2 promoter, whereas in the absence of any coeffector or in the presence of
phenylalanine, the TyrR protein inhibits a step(s) following the formation
of open complexes. We also present mutational evidence which implicates th
e N-terminal domain of the TyrR protein in the repression of P2 expression.
The TyrR binding site of aroP, which includes one weak and one strong TyrR
box, is located 5 bp downstream of the transcription start site of P2. Res
ults from a mutational analysis show that the strong box (which is located
more closely to the P2 promoter), but not the weak box, plays a critical ro
le in P2 repression.