Peptide mapping of 125I-labelled influenza virus proteins. Matrix proteins as markers in recombination

Protein and nucleic acid analysis of influenza B viruses isolated in Italy in 1984

Genomic and phenotypic analysis of 30 influenza B viruses, isolated in Italy in 1984, antigenically closely related to the B/USSR/100/83 prototype virus, was carried out using T1-oligonucleotide fingerprinting of total RNA and one-dimensional peptide mapping. The results of fingerprinting analysis indicated an oligonucleotide spot homology of 90-96%, corresponding to a nucleotide sequence variation of only 0.75-0.3%. All the strains appear to belong to the same evolutionary line. Nevertheless, heterogeneity was found at the structural and antigenic level, when the viruses were compared by peptide mapping and monoclonal antibody analysis. No correlation between the biochemical variability of the viruses and the epidemiological characteristics of the different strains was established, which is consistent with the hypothesis that distinct variants, arisen at different times from a parental strain, co-circulate during an epidemic, although the additional occurrence of random mutations during the evolution of the epidemic cannot be excluded.

Antigenic characterization of influenza A virus matrix protein with monoclonal antibodies

Monoclonal antibodies were used to study antigenic variation in three distinct epitopes on the matrix protein of influenza A viruses. We found that two of these epitopes underwent antigenic variation, but in a very limited number of virus strains. A third epitope appeared to be an invariant type-specific determinant for influenza A viruses. Competitive antibody binding assays and Western blot analysis of proteolytically digested matrix protein indicated that at least two of the three epitopes are located in nonoverlapping domains on the matrix protein molecule.

Peptide mapping of 125I-labelled membrane protein of influenza viruses by reverse-phase high-performance liquid chromatography

The resolution potential of reverse-phase high-performance liquid chromatography (HPLC) for peptide analysis of hydrophobic viral membranes has been investigated, using as model the membrane (M) protein of influenza virus. Proteolytic digests of 125I-labelled M protein and CNBr fragments, extracted from radioiodinated whole virus, have been separated on a uBondapak C18 column with an isopropanol or acetonitrile solvent system. Peptide mapping of trypsin digests of M protein from A/PR/8/34 (H1N1) and A/chicken/Germany/N/49 (H10N7) viruses was identical, whereas Staphylococcus aureus V8 protease digests showed minor differences in at least two peptides. The results also show that HPLC is a powerful tool for the separation of proteolytic digests of viral proteins, since the peptide maps are highly reproducible and recovery was greater than 85%.

Genetic variability of Hong Kong (H3N2) influenza viruses: spontaneous mutations and their location in the viral genome

The genetic heterogeneity of five influenza A (H3N2) strains isolated between 1968 and 1977 has been estimated by T1-oligonucleotide fingerprinting of 32P-labeled viral RNA. Assuming that the large T1-resistant oligonucleotides represent a random sample of the viral RNA, the genetic differences observed would affect 0.3 to 10.7% of the RNA positions of the genes studied, depending on the pair of viruses considered. A smaller degree of genetic heterogeneity was observed when six coetaneous viral samples were compared. The distribution of spontaneous mutations among the viral genes was studied by fingerprinting individual RNA segments isolated either by gel electrophoresis or hybridization with plasmids containing influenza-specific DNA sequences. No statistically significant differences were detected in the distribution of mutations among the viral genes studied. The mutation frequency at the hemagglutinin RNA region coding for the HA1 subunit was found to be two times higher than that at the region encoding that HA2 subunit. Our results suggest that the antigenic variability of influenza viruses may be a consequence of a general genetic variability which effects many of the viral genes.