Abstract
Temperature sensitive mutants of bacteriophage Q have been isolated which fail in the synthesis of their virus RNA at the non-permissive temperature (42 °C). Nine mutants have been studied in some detail. Cells infected with these mutants at 37 °C and incubated long enough to produce substantial amounts of Q RNA cease Q RNA replication when shifted to 42 °C. The mutants can be classified into 3 groups according to the amount of Q RNA replicase activity exhibited in extracts from infected cells isolated at various times after shift to 42 °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 °C in cells infected with group 1 or group 3 mutants. In cells infected with group 2 mutants, synthesis of Q RNA replicase subunit is increased, but synthesis of other virus proteins is depressed at 42 °C. The inhibition of virus RNA and protein synthesis is reversible. A detailed analysis of these experiments suggests that a defective Q RNA replicase is involved in the inhibition of both virus RNA and protein synthesis.
* Present address: Department of Molecular Biology, Albert Einstein College of Medicine, New York City, N.Y. 10461.
† Present address: Department of Microbiology, The University of New Mexico, School of Medicine, Albuquerque, New Mexico 87106.