Polar effects of an amber mutation in f2 bacteriophage

Abstract

Bacteriophage f2 mutant sus-3, containing an amber mutation near the N-terminus of the coat protein cistron, is polar. Bacteria infected by sus-3 synthesize little RNA polymerase or viral RNA. RNA from infecting phage is incorporated into a double strand only 15 to 25% as well as is RNA from normal virus. Suppression of the amber mutation results in a two- to fourfold increase in the amount of parental sus-3 double-stranded RNA. Two independent experiments established that the sus-3 amber mutation has no effect on the ability of double-stranded RNA to function in phage RNA replication, in contrast to our previous prediction (Lodish & Zinder, 1966 b). All of the polar effects of the sus-3 mutation can be ascribed to decreased synthesis of the enzyme required for the first step of RNA replication (production of complementary RNA). The results eliminate explanations of polarity which postulate a coupling between translation and synthesis of virus RNA.