Localization of the Escherichia coli RNA polymerase β′ subunit residue phosphorylated by bacteriophage T7 kinase Gp0.7

During bacteriophage T7 infection, the Escherichia coli RNA polymerase β′ subunit is phosphorylated by the phage-encoded kinase Gp0.7. Here, we used proteolytic degradation and mutational analysis to localize the phosphorylation site to a single amino acid, Thr¹⁰⁶⁸, in the evolutionarily hypervariable segment of β′. Using a phosphomimetic substitution of Thr¹⁰⁶⁸, we show that pliosphorylation of β′ leads to increased ρ-dependent transcription termination, which may help to switch from host to viral RNA polymerase transcription during phage development.