- Volume 67, Issue 7, 1986

The IgG subclass specificity of Fc receptor(s) induced on cells by infection with human cytomegalovirus (HCMV) was studied in a binding assay by using infected cells and purified iodinated IgG of various subclasses from HCMV seronegative healthy adult donors. All four human IgG subclasses bound to HCMV-infected cells, with the following relative magnitudes: IgG1 ⩾ IgG4 > IgG2 > IgG3. The IgG subclass specificity of the Fc receptor was further analysed in an inhibition assay by using fragments prepared from purified human IgG by papain digestion, and using unlabelled subclass proteins. Fc but not Fab fragments inhibited the binding of 125I-labelled human IgG to HCMV-infected cells. The biological role of the Fc receptor in HCMV infection is discussed.

A virus-neutralizing monoclonal antibody (1E3) specifically immunoprecipitated the 70000 mol. wt. (70K) fusion (F) protein from respiratory syncytial (RS) virus-infected HeLa cells. Western blotting analysis of polypeptides from such cells separated by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions revealed that 1E3 was peculiar in that it bound to both F1 (50K) and F2 (20K) components of the F protein. Antibody subsequently eluted from either the F1 or the F2 regions of immunoblots re-bound to both F1 and F2 regions of the SDS-PAGE blot. These results show that monoclonal antibody 1E3 reacts with an epitope which is found on both F1 and F2 subunits of RS virus fusion protein.

High multiplicity BK virus (BKV) infection of primary cells derived from human foetal pancreas resulted in massive cytopathology and subsequent outgrowth of cells. Intranuclear BKV T-antigen was present in all cells and viral antigen was detected in 10 to 30% of these cells. The subcultured cells yielded BKV in the supernatant (approx. 105 TCID50/ml) and in the cells free viral DNA was present (approx. 10% of total cellular DNA content). Analysis of the viral DNA indicated the presence of deleted and rearranged BKV DNA molecules. Although all cells continuously expressed BKV T-antigen they did not exhibit the transformed phenotype. This persistent infection of human foetal pancreas cells represents a novel type of in vitro interaction between BKV and human cells which may correspond to the in vivo findings on BKV tropism for pancreatic cells.

Filamentous particles of rice stripe virus (RSV) were found to be associated with an RNA-dependent RNA polymerase activity. The enzyme catalysed the synthesis in vitro of single- and double-stranded RNAs corresponding in size with RNA found in RSV particles, as well as two other dsRNAs with mol. wt. of 1.0 × 106 and 0.56 × 106. The RSV polymerase activity required Mg2+, Mn2+ or Fe2+ but not Na+, K+ or NH+ 4 which were inhibitory at concentrations of more than 50 mm. The optimum pH of the polymerase was around 8.0 at the optimum temperature, 40°C. Detergent treatment of RSV particles did not enhance the polymerase activity. Purified RSV particles contained a minor polypeptide (mol. wt. 230000) as well as coat protein; the former may be the RSV polymerase. The taxonomy of RSV is discussed in relation to enveloped animal viruses with negative-stranded RNA, which also contain an RNA-dependent RNA polymerase in virus particles.

The sequence of the 4662 nucleotides [excluding poly(A)] of RNA-2 of tomato black ring virus (TBRV) has been determined. Most of the sequence (4074 nucleotides) encodes a polypeptide of mol. wt. 150000 (150K). The 5′ and 3′ non-coding sequences are 287 and 301 nucleotides in length, differ from the coding sequence in base composition, and contain repeated sequences, some of which resemble oligonucleotides in the 3′ non-coding sequence of M-RNA of cowpea mosaic virus (CPMV). From its amino acid composition, the coat protein of TBRV was tentatively located in the C-terminal third of the 150K polypeptide. The amino acid sequence of the 150K polypeptide immediately N-terminal to the putative coat protein sequence was found to resemble parts of the 30K polypeptides of tobamoviruses and, to a lesser extent, part of the 105K polypeptide translation product of CPMV M-RNA.

Genome fragments from two serotypes of barley yellow dwarf virus (BYDV) were cloned and used as hybridization probes. Dot blot assays using 32P-labelled plasmid probes readily detected BYDV in crude sap extracts from infected plants and were at least as sensitive as ELISA. Some clones were specific for either the RPV or the PAV serotypes. Others hybridized not only with the RNA of both serotypes but also with those of three other luteoviruses (beet western yellows, potato leaf roll and soybean dwarf), but they did not hybridize with the RNA of a tobamovirus or Escherichia coli tRNA. These nucleic acid probes therefore have potential for the general diagnosis of infection by members of the luteovirus group as well as detection of specific BYDV serotype infections. The taxonomic implications of the observation that the genomes of different luteoviruses have some conserved regions are discused.

Mutants of cauliflower mosaic virus (CaMV), generated in vitro by modification of recombinant DNA plasmids containing the viral genome, either retained the ability to induce disease symptoms on turnip plants, produced less severe symptoms or failed to induce symptoms. Wild-type symptoms were produced by a variant CaMV DNA of the Cabbage S isolate that had 4 bp in open reading frame (ORF) III replaced with a 16 bp sequence. Less severe symptoms, due to a delay in symptom appearance relative to inoculation with wild-type DNA, were induced by a mutant with a frameshift mutation in ORF II (pSA103). CaMV DNA, recovered from plants infected with pSA103, contained a second mutation which restored the original translation reading frame. Nucleic acid hybridization to ‘squishes’ of leaf tissue from plants that had been inoculated with mutant DNAs that included DNAs modified in each of the six major ORFs of CaMV DNA revealed that only those plants that appeared diseased had detectable CaMV nucleic acid in uninoculated leaves. Replicated CaMV DNA was also not detected in non-encapsidated and virion DNA fractions from inoculated leaves of non-diseased plants.