Plaque-size Mutants obtained from the Ribonucleic Acid Phage fr after Treatment with Nitrous Acid

Abstract

PHAGE fr (formerly ft 5 (ref. 1)) in its characteristics² is related to f-phages described by Loeb and Zinder³. For the initiation of genetical studies, attempts were made to obtain mutants from phage-suspensions treated with nitrous acid. Conditions of treatment were essentially those described by Schuster and Schramm⁴. Single-hit kinetics of inactivation was established over a range of 5 logarithmic cycles. Standard phage techniques⁵ were used. Since the rate of inactivation is exponential in relation to the time of incubation in nitrous acid, the inactivation is characterized by the ‘reduced time’ τ= e⁻¹. When suspensions of fr were inactivated at 37° C and pH 4.28 by 0.5 M sodium nitrite, τ equalled 3.5 min. A comparison with the rates of inactivation by nitrous acid as reported for other viruses is shown in Table 1. It demonstrates that the τ of inactivation of phage fr is more closely of the order of the τ of tobacco mosaic virus (TMV) than that of DNA-phages.