R17 RNA replicase. V. Rifamycin sensitivity of R17 RNA synthesis in vivo

The effect of rifamycin on R14 phage growth in vivo was examined using rifamycin sensitive and resistant strains of E. coli as host cells. The following conclusions were obtained: (1) There is a time lag between the addition of rifamycin to the culture and the initiation of inhibitory action by the drug. At 25 mug rifamycin per ml, this time lag is approximately 30 min. At 50 mug per ml, it takes 10 min to exert 90% inhibition of RNA synthesis in both infected and non-infected cultures. (2) The rifamycin sensitive stage for R17 growth is the first 20 min of its infectious cycle during which time the synthesis of phage components, but not the assembly, takes place. (3) Of the phage component synthesis, RNA synthesis is definitely sensitive to rifamycin in contrast to the other RNA phage systems. Of the four phage specific RNA's, progeny plus strand synthesis is trongly inhibited. The synthesis of replicating forms is also sensitive to rifamycin, but their suppression appears to be incomplete.