Studies of temperature sensitive mutants of bacteriophage Qbeta, defective in both replication and translation

Temperature sensitive mutants of bacteriophage Qbeta have been isolated which fail in the synthesis of their virus RNA at the non-permissive temperature (42 degrees C). Nine mutants have been studied in some detail. Cells infected with these mutants at 37 degrees C and incubated long enough to produce substantial amounts of Qbeta RNA cease Qbeta RNA replication when shifted to 42 degrees C. The mutants can be classified into 3 groups according to the amount of Qbeta RNA replicase activity exhibited in extracts from infected cells isolated at various times after shift to 42 degrees C: in group 1 mutants, enzyme activity is the same, regardless of the time of isolation after shift; in group 2 mutants enzyme activity increases with time of isolation after shift; in group 3 mutants, enzyme activity decreases with time of isolation after shift. Synthesis of all virus proteins is suppressed at 42 degrees C in cells infected with group 2 of group 3 mutants. In cells infected with group 2 mutants, synthesis of Qbeta RNA replicase subunit beta is increased, but synthesis of other virus proteins is depressed at 42 degrees C. The inhibition of virus RNA and protein synthesis is reversible. A detailed analysis of these experiments suggests that a defective Qbeta RNA replicase is involved in the inhibition of both virus RNA and protein synthesis.