Three cistrons in bacteriophage Qβ

Amber mutants of bacteriophage Qβ were isolated and classified into three groups by complementation tests. Physiological studies showed that the three cistrons of Qβ could be related to the three known genes of the f2 group of RNA phages. Gene I mutants do not produce either phage RNA polymerase or phage specific RNA in Su − hosts. Gene II mutants in Su − hosts produce defective phage particles which are lighter in density than viable phage particles. Gene III mutants do not grow on either Su-2 or Su-3 suppressor strains; they hyperproduce double-stranded RNA and viral RNA polymerase on these hosts. On Su − hosts they appeared to have a polar effect on the synthesis of phage RNA polymerase. None of the Qβ mutants lysed nonpermissive hosts.