Host-bacteriophage interaction in Agrobacterium tumefaciens. I. Characterization of bacteriophage R4 and physiological changes in the infected host cell.

Infection of Agrobacterium tumefaciens B6, a tumor-producing plant pathogen, by bacteriophage R4, does not immediately shut off host deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and protein synthesis. Viral DNA synthesis begins soon after infection, but the host DNA is not shut off until after 35 min; net RNA and protein synthesis are not inhibited until 30 min after infection. The pattern of synthesis of phage particles was confirmed by electron microscopy of thin sections during the infection cycle. The phage particle consists of a polyhedral head, 65 nm in diameter, and a long flexible tail 210 nm long and 10 nm wide with helically arranged subunits. By gel electrophoresis, four major protein components with the following molecular weights were found in the capsid: 72,000, 45,000, 28,000, and 14,500. The phage DNA has a molecular weight of 30 million and a guanine-cytosine content of 59%.