Physiological study of cooperative infection by restricted bacteriophage T1

The ability of certain phages to successfully infect a restricting host at a high multiplicity of infection is known as cooperative infection or cooperation. We have examined the ability of unmodified T1 (T1.0) to participate in cooperative infection in cells possessing the P1 restriction system. We have found that cooperation is dependent upon protein synthesis during the first few minutes after phage infection. However, we have been unable to attribute the necessary protein to a known T1 cistron. Degradation of the restricted T1 genome is approximately equally extensive whether cooperative infection occurs or whether it is blocked by chloramphenicol. It is postulated that an inducible host repair mechanism may be responsible for the phenomenon of cooperative infection.