6 Morphogenesis of RNA Phages

Abstract

1. INTRODUCTION
The RNA phages are the simplest phages known so far. They are composed of only three components, coat protein, A protein¹ and RNA. They are, therefore, promising models for phage morphogenesis. Nevertheless, we do not yet fully understand the sequential steps in phage assembly, and what we present here are thus only the most probable mechanisms of morphogenesis.

The study of phage morphogenesis can be approached in the following ways:One can study the process of morphogenesis by observing events occurring in vivo, possibly employing cells with artificially treated envelopes that become penetrable to macromolecules such as proteins, nucleic acids and antibiotics.

One can use unfractionated (“ex vivo”) cell extracts.

Fractionation of viral particles or of “ex vivo” extracts will lead to defined components which can be used in in vitro systems.

All these systems have advantages. While in vivo, processes occur under the most natural conditions, important steps in morphogenesis proceed too fast, without synchrony and against a background of cell material too high to permit application of sensitive biophysical techniques. Inhibition of the synthesis of specific components of the morphogenesis system can be achieved either by starvation, the action of antibiotics, or the use of phage mutants. Defective structures may accumulate which one may hope to convert to viable phage after restoration of normal conditions. If the fate of radioactive label is to be followed, one may reduce the background of labeled host components with inhibitors of cellular nucleic acid metabolism (actinomycin, the...