title: [Molecular mechanisms of reversions to the ts+ -phenotype of cold-adapted influenza virus A strains--attenuation donors for live influenza reassortant vaccines].
abstract: A ts+ revertant of cold-adapted (ca) strain A/Leningrad/134/47/57--the attenuation donor for live influenza reassortant vaccines--was obtained by passages of the ca strain in chick embryos at nonpermissive temperatures. The ts+ revertant acquired the ability to grow in chick embryos at 40 degrees C and lost the capacity to reproduce there at 25 degrees C. A complementation-recombination test using the fowl plague virus (FPV0 ts-mutants showed the loss of the ts-phenotype in the RNA-segments of ts+ revertants' genome coding for PB2, NP, and NS (NS2) proteins. However, PCR-restriction analysis revealed a true reversion in RNA-segment coding for PB2 protein only. All the investigated mutations in the ts+ revertant genome were preserved. This phenomenon could be explained by the appearance of intragenic and extragenic suppression mutations in the ts+ revertant genome. The data of the complementation-recombination test suggest that reversion of ts-phenotype occurs more frequently due to extra- or intragenic suppression rather than as a result of a true mutation loss. Estimation of the genetic stability of vaccine ca strains of influenza virus should be based on the combined use of PCR-restriction and complementation tests.
authors.forename: S G
authors.initials: SG
authors.lastname: Markushin
authors.forename: I I
authors.initials: II
authors.lastname: Akopova
authors.forename: I B
authors.initials: IB
authors.lastname: Koptiaeva
authors.forename: T M
authors.initials: TM
authors.lastname: Tsfasman
authors.forename: Iu Z
authors.initials: IuZ
authors.lastname: Gendon
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D002642:Chick Embryo; D005816:Genetic Complementation Test; D006358:Hot Temperature; D053121:Influenza A Virus, H2N2 Subtype / Q000235:genetics* / Q000502:physiology; D016133:Polymerase Chain Reaction; D016865:Reassortant Viruses / Q000235:genetics* / Q000502:physiology; D011995:Recombination, Genetic; D012692:Serial Passage; D013489:Suppression, Genetic; D014764:Viral Proteins / Q000235:genetics; D014779:Virus Replication
chemical_list: C502893:PB2 protein, influenza virus; D014764:Viral Proteins