T7 development inEscherichia colirequires 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 growingE. colias a consequence of buildup of guanosine pentaphosphate ((p)ppGpp) during T7 development. We further demonstrate a requirement of Gp5.7 for T7 development inE. colicells 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.Significance statementVirus that infect bacteria (phages) represent the most abundant living entities on the planet and many aspects of our fundamental knowledge of phage-bacteria relationships have been derived in the context of exponentially growing bacteria. In the case of the prototypicalEscherichia coliphage T7, specific inhibition of the housekeeping form of the RNA polymerase (Eσ70) by a T7 protein, called Gp2, is essential for the development of viral progeny. We now reveal that T7 uses a second specific inhibitor that selectively inhibits the stationary phase RNAP (EσS), which enables T7 to develop well in exponentially growing and stationary phase bacteria. The results have broad implications for our understanding of phage-bacteria relationships and therapeutic application of phages.
Contacts between Escherichia coli RNA polymerase and an early promoter of phage T7.