The phage growth limitation system in Streptomyces coelicolor A(3)2 is a toxin/antitoxin system, comprising enzymes with DNA methyltransferase, protein kinase and ATPase activity

The phage growth limitation system of Streptomyces coelicolor A3(2) is an unusual bacteriophage defence mechanism. Progeny ϕC31 phage from an initial infection are thought to be modified such that subsequent infections are attenuated in a Pgl(+) host but normal in a Pgl(-) strain. Earlier work identified four genes required for phage resistance by Pgl. Here we demonstrate that Pgl is an elaborate and novel phage restriction system that, in part, comprises a toxin/antitoxin system where PglX, a DNA methyltransferase is toxic in the absence of a functional PglZ. In addition, the ATPase activity of PglY and a protein kinase activity in PglW are shown to be essential for phage resistance by Pgl. We conclude that on infection of a Pgl(+) cell by bacteriophage ϕC31, PglW transduces a signal, probably via phosphorylation, to other Pgl proteins resulting in the activation of the DNA methyltransferase, PglX and this leads to phage restriction.