T7 development in Escherichia coli requires the inhibition of the housekeeping
form of the bacterial RNA polymerase (RNAP), Eσ70, by two T7 proteins: Gp2
and Gp5.7. While the biological role of Gp2 is well understood, that of Gp5.7
remains to be fully deciphered. Here, we present results from functional and
structural analyses to reveal that Gp5.7 primarily serves to inhibit EσS, the
predominant form of the RNAP in the stationary phase of growth, which
accumulates in exponentially growing E. coli as a consequence of buildup of
guanosine pentaphosphate ((p)ppGpp) during T7 development. We further
demonstrate a requirement of Gp5.7 for T7 development in E. coli cells in the
stationary phase of growth. Our finding represents a paradigm for how some
lytic phages have evolved distinct mechanisms to inhibit the bacterial
transcription machinery to facilitate phage development in bacteria in the
exponential and stationary phases of growth.