A simple procedure for the analysis of the structural proteins of influenza and parainfluenza viruses involving adsorption to erythrocytes

Interference by a non-defective variant of influenza A virus is due to enhanced RNA synthesis and assembly

Mouse-adapted influenza A virus, FM-MA, interferes with the replication of wild-type strains on co-infection. The interference phenotype was previously mapped to FM-MA segment 2 encoding a mutant PB1 protein, the catalytic component of the RNA polymerase complex. To identify the point at which FM-MA interferes with wild-type A/HK/1/68 (HK), the relative levels of transcription and genome replication of the PB1, NP and M1 genes were determined for FM-MA and HK viruses in co-infected cells using RT-PCR. All stages of HK macromolecular synthesis (primary and secondary transcription, genomic RNA, complementary RNA and protein synthesis) were suppressed relative to FM-MA. Infection with HK virus alone resulted in the accumulation of similar or greater amounts of RNA at late times post-infection relative to FM-MA thus indicating that the presence of FM-MA specifically compromised HK transcription and replication in co-infected cells. However early in infection FM-MA was ten times more active in mRNA transcription than HK or its parental strain FM. FM-MA's ability to interfere was primarily due to an increased capacity for primary transcription. FM-MA genomes were also selectively assembled into progeny virus from cells co-infected with HK and FM-MA, a step which was distinct from the capacity for enhanced RNA synthesis. This suggests that interference of HK growth by FM-MA in mixed infections results from two distinct events: a preferential synthesis of FM-MA-specific macromolecules which is then augmented by a preferential assembly of FM-MA genomes.

Genetic variants of influenza A/Taiwan/1/86 cocirculating in Canada during the winter of 1986 to 1987

The first isolate of influenza virus in Canada during the winter of 1986 to 1987 was a genetic variant of A/Taiwan/1/86. This genetic variant type was the predominant strain obtained from several of the western provinces. The variant strains were antigenically indistinguishable from A/Taiwan/1/86 but were remarkably distinct by T1 oligonucleotide mapping. T1 mapping of individual genome segments indicated that the variants evolved from an A/Taiwan/1/86-like virus through the accumulation of point mutation or deletion or insertion events and probably do not contain foreign genes. The relative distribution of genetic variation was approximately equal among the individual genes, with the possible exception of segments 1 or 2 that were analyzed in combination and thus could not be individually associated with the observed variation.

Persistent infections with Sendai virus and Newcastle disease viruses

Persistent infections (Pi) were established in two host-cell systems [Madin-Darby bovine kidney (MDBK) and Madin-Darby canine kidney (MDCK)] with Sendai virus and three strains of NDV, to test the influence of different viruses and host-cell systems. Virus was recovered from the persistently infected cells. An RNA- ts mutant was recovered from a Pi of MDBK cells, but no Pi could be established in MDCK cells with the three strains of NDV. Additionally, the Pi was established exclusively by a virulent strain, NDV-Milano. On the other hand, Sendai virus could establish Pi in MDBK and MDCK cell-systems. Several ts mutants were recovered from "late" passages of Pi, and from an accidental infection, a ts mutant with an altered P polypeptide. Ten other ts mutants were tested, however, the specific ts lesion could not be identified. From three Pi in MDCK cells, host range mutants (ts-f1, ts-f2, and ts-f3) were recovered. One of the mutants (ts-f1) has an altered M (matrix) protein. The host range mutants undergo a productive infection in MDBK and MDCK cells, which are nonpermissive for wild type Sendai virus. The possible significance of the results are discussed.

Persistence of mumps virus in mouse L929 cells

The characteristics of a persistent infection of L929 cells with mumps virus (MuV) is presented. The persistent infection (L-MuV cells) was regulated by interferon (IFN) produced endogenously and almost all the properties showed that the carrier culture was maintained by horizontal transmission of the virus. Small-plaque mutants, but not temperature-sensitive variants, were selected during the persistent infection. MuV released from L-MuV cells (MuV-pi) replicated efficiently in L929 cells, while infection of L929 cells with the original MuV-o resulted in an abortive infection. The efficient replication of MuV-pi in L929 cells can be explained by the findings that MuV-pi induced IFN more slowly and had lower susceptibility to IFN in L929 cells than MuV-o did. M protein was synthesized to a considerable degree in MuV-pi-infected cells, while it could not be detected in MuV-o-infected cells. By contrast, MuV-pi formed small plaques in Vero cell monolayers and the yield of MuV-pi in Vero cells was lower than that of MuV-o. M protein induced by MuV-pi decayed easily in Vero cells. M protein was considered to be a limiting factor for MuV replication in both cell lines.