Temperature-Sensitive Mutants Isolated from L Cells Persistently Infected with Newcastle Disease Virus

Abstract

Virus mutants (NDV pi ) isolated from L cells persistently infected with the Herts strain of Newcastle disease virus have been previously reported by this laboratory to differ from the wild-type virus (NDV o ) in several physical and biological properties. It has now been determined that, in addition to these differences, the NDV pi mutants are also spontaneously selected temperature-sensitive mutants. The temperature sensitivity of 10 NDV pi clones was confirmed by temperature inhibition, plaquing efficiency, and single-cycle yield experiments. The cut-off temperature, at which more than 90% of virus replication is inhibited was between 41 and 42 C. All 10 NDV pi clones were also found to be defective in virus-specific ribonucleic acid (RNA) synthesis in infected chick embryo cells at 42 C and are tentatively classified as RNA − . The possible relationships of the temperature sensitivity, the other NDV pi properties, and the maintenance of the persistently infected state are discussed.