Studies on a Temperature-sensitive Mutant of Fowl Plague Virus Having a Mutation in Gene 7 Coding for the M Protein

Research Institute for Viral Preparations, Moscow, U.S.S.R. A fowl plague virus (FPV) temperature-sensitive mutant, ts 303/1 having a ts mutation in gene 7 coding for the matrix (M) protein has been obtained. The mutant induced synthesis of virus-specific RNA and polypeptides as well as ribonuclear protein (RNP) formation in cells under non-permissive conditions; however, haemagglutinin cleavage was reduced, functionally active haemagglutinin and neuraminidase were absent and virions were not formed. In mutant-infected cells at 36 °C haemagglutinin cleavage was also reduced and virions formed had an altered NP:M ratio as well as a decreased haemagglutinin content. A population of virions formed under these conditions was heterogeneous both in morphology and in buoyant density. The data obtained suggest that a mutation in the M proteins of orthomyxoviruses can affect processing of the haemagglutinin and impair final stages of virion morphogenesis. Keywords: orthomyxoviruses, fowl plague virus, ts mutants, M protein Received 22 April 1982; accepted 31 August 1982.