Sequential steps in the in vivo assembly of the RNA bacteriophage fr

Non-infectious phage-like particles form during histidine starvation in bacteria infected with the RNA bacteriophage fr. As judged by their sedimentation velocity, CsCl buoyant density and ribonuclease sensitivity, these particles resemble defective phage particles produced by phage assembly amber mutants in suppressor negative host bacteria. Defective phage particles are not converted to infectious phages if the synthesis of the histidine-containing maturation protein is resumed in the host cells. Furthermore, arguments have been provided that viral messengers which are repressed for the biosynthesis of the viral RNA synthetase—presumably by specific combination with a few subunits of the main coat protein—might not be incorporated into infective particles. The results suggest that association of viral RNA molecules with histidine containing maturation protein is required as an early step in the process of phage maturation.