C. Jourlin et al., TRANSPHOSPHORYLATION OF THE TORR RESPONSE REGULATOR REQUIRES THE 3 PHOSPHORYLATION SITES OF THE TORS UNORTHODOX SENSOR IN ESCHERICHIA-COLI, Journal of Molecular Biology, 267(4), 1997, pp. 770-777
Two-component regulatory systems allow cells to adapt to environmental
changes. In Escherichia coli, the TorS/TorR two-component system indu
ces the expression of the tor structural operon encoding the trimethyl
amine N-oxide reductase respiratory system in response to substrate av
ailability. TorS belongs to a sensor subfamily that includes a classic
al transmitter domain, a receiver, and a C-terminal alternative transm
itter domain. The histidine phosphorylation sites of each TorS transmi
tter domain and the aspartate phosphorylation site of the TorS receive
r were individually changed by site-directed mutagenesis. All three ph
osphorylation sites proved essential for in vivo induction of the tor
structural operon and for in vitro transphosphorylation of the cognate
TorR response regulator. The His to Gin change in the classical trans
mitter domain abolished TorS autophosphorylation, whereas TorS underwe
nt significant autophosphorylation when the phosphorylation site of it
s receiver or alternative transmitter was changed. Complementation bet
ween pairs of defective TorS proteins was achieved in vitro, allowing
TorR transphosphorylation. This strongly suggests that TorS is a multi
mer in which intermolecular phosphorylation occurs. The wild-type alte
rnative transmitter domain alone was shown to complement a TorS protei
n mutated in its C-terminal alternative transmitter. Interestingly, ov
erproduction of the alternative transmitter domain led to in vivo TorR
-dependent constitutive expression of the tor operon in a torS(+) or t
orS context. Hence, the TorS alternative transmitter contains the phos
phodonor site for TorR. Taken together, our results support a TorS pho
sphorylation cascade from the classical transmitter to the sensor rece
iver and the alternative transmitter phosphorylation sites. (C) 1997 A
cademic Press Limited.