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Studies of Temperature Sensitive Mutants of Bacteriophage Q, Defective in both Replication and Translation

R. J. Radloff

Biophysics Laboratory of the Graduate School and Biochemistry Department of the College of Agricultural and Life Sciences, University of Wisconsin, Madison, Wisconsin 53706, U.S.A.

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.

Received 4 February 1975; accepted 30 April 1975.