Some bacterial toxins are produced only when the bacteria are infected with viruses. The ultimate objective of this research is to understand how toxin production is controlled in virus-infected cells. This broad objective can be initially studied in cells infected with toxinogenic Corynebacteriophage. The immediate objectives are 1) to determine the component of diphtheria toxin which is active in controlling bacterial protein synthesis and to study its specificity and mechanism of action. The effects of toxin, toxin fragments or mutant toxin proteins on an in vitro protein synthesizing system derived from uninfected Corynebacterium diphtheriae will be examined. This system will be primed with either host cell or viral messenger RNA. The in vitro protein synthesizing system will be fractionated in order to identify which component is affected by toxin; 2) to determine the role of toxin or toxin fragments as viral structural proteins. Our recent identification of toxin and fragment B in purified Corynebacteriophage will be extended to include morphological studies in order to relate the location and quantity of these molecules to specific phage structure. Various mutant phages which produce altered toxins will also be examined; 3) to study the iron-induced toxin "inhibitory protein." The size and complexity of the purified "inhibitory protein" will be determined on SDS-polyacrylamide gels and by analytical ultracentrifugation. Its specificity and mechanism of action will also be studied, both in an in vitro protein synthesizing system and by examining the interaction of inhibitory protein and isolated RNAs; 4) to determine how strain variation in toxin production affects phage biosynthesis. The rate of production and final yields of toxin and toxin fragments will be quantitated in different strains of C. diphtheriae infected with a hypervirulent toxinogenic phage and correlated with the yields of total and infectious phage particles produced.