J. Gowrishankar et Aj. Pittard, Superimposition of TyrR protein-mediated regulation on osmoresponsive transcription of Escherichia coli proU in vivo, J BACT, 180(24), 1998, pp. 6743-6748
Osmotic regulation of proU expression in the enterobacteria is achieved, at
least in part, by a repression mechanism involving the histone-like nucleo
id protein H-NS. By the creation of binding sites for the TyrR regulator pr
otein in the vicinity of the sigma(70)-controlled promoter of proU in Esche
richia coli, we were able to demonstrate a superposed TyrR-mediated activat
ion by L-phenylalanine (Phe), as well as repression by L-tyrosine, of proU
expression in vivo. Based on the facts that pronounced activation in the pr
esence of Phe was observed even at a low osmolarity and that the affinity o
f binding of TyrR to its cognate sites on DNA is not affected by Phe, we ar
gue that H-NS-mediated repression of proU at a low osmolarity may not invol
ve it classical silencing mechanism. Our data also suggest the involvement
of recruited RNA polymerase in the mechanism of antirepression in E. coli.