- Volume 71, Issue 12, 1990

Transcripts from two immediate early (IE) genes have been identified in cells infected with the gammaherpes- virus, herpesvirus saimiri. One is a 1·3 kb RNA transcribed from the HindIII-G fragment of virus DNA (IE-G), the other is a 1·6 kb RNA from the gene for the IE 52K phosphoprotein. Labelled oligonucleotide probes specific for each of these RNAs have been used in in situ hybridization experiments to compare their expression in individual cells in infected populations. In the presence of cycloheximide, the IE-G RNA accumulates synchronously throughout the population of infected cells and prior to the asynchronous accumulation of RNA from the gene for the IE 52K protein in the same population of cells. This heterogeneity in the timing of expression of RNA from the IE 52K gene is paralleled by the asynchronous accumulation of the protein product. We conclude that transcription of the IE-G RNA is independent of expression of the IE 52K gene and that expression of the 52K gene requires (or is prevented by) factors which do not affect accumulation of the RNA from the IE-G gene.

The nucleotide sequence was determined for the fusion (F) protein-coding mRNA of the bovine respiratory syncytial virus (strain RB 94) and the amino acid sequence of the F protein was deduced for comparison with the sequence of human respiratory syncytial virus subtypes A and B (RSS-2 and 18537 strains). The human and bovine RS virus F proteins (excluding the cleaved signal peptide) share 83 to 84% homology. The greatest divergence occurred within the F2 subunit in the region preceding the cleavage activation site.

The sequence of the 22K mRNA of strain 18537 of antigenic subgroup B of human respiratory syncytial virus (RSV) was determined by sequencing cloned cDNAs of intracellular mRNA. Comparison with the corresponding sequence of the A2 strain of subgroup A showed that there is 78% nucleotide sequence identity overall, that the amino acid sequence of the 22K protein is 92% identical between subgroups and that the 22K mRNA of both subgroups contains a second, internal, overlapping open reading frame (ORF) whose length, nucleotide sequence and potential translational start and stop sites were highly conserved and whose predicted product has 62% amino acid identity between subgroups. Sequence analysis of 36 cDNAs of intracellular 22K mRNA of strain A2 did not detect nucleotide insertions or deletions in the region of overlap between the two ORFs, indicating that the majority of intracellular 22K mRNA is a faithful copy containing the two distinct ORFs. Translation in vitro of mRNAs transcribed from engineered cDNAs showed that an mRNA which contained only the second, internal ORF directed the synthesis of a previously unidentified polypeptide of the predicted size, whereas mRNA representing the complete gene directed the synthesis of both the 22K protein and the product of the internal ORF. This latter species was synthesized in vitro as a discrete, separate protein rather than as a fusion protein. It is not yet known whether this protein is synthesized in RSV-infected cells.

The effect of a series of antisense oligodeoxyribonucleotides [oligo(dN)] on the expression of the surface antigen (HBsAg) gene of human hepatitis B virus (HBV) was examined using hepatocellular carcinoma cells that contain integrated HBV genomes. Of a number of antisense oligo(dN)s tested, synthetic 15-mers directed at the cap site of mRNA and regions of the translational initiation site of the HBsAg gene were found to be highly effective and inhibited viral gene expression by as much as 96 %. The inhibition was specific to the HBsAg gene and appeared to be at the level of translation. These results suggest a therapeutic potential for antisense oligo(dN) in the treatment of patients who are chronically infected with HBV.

cDNA fragments of a 5′-terminal region of the hepatitis C virus (HCV) genome were isolated by the reverse polymerase chain reaction from RNA extracted from plasma samples of healthy Japanese carriers. Their nucleotide sequence was compared with that of the original isolate which had been passaged twice in chimpanzees. No deletions or insertions were observed between the two sequences in the regions examined. Both the 5′ untranslated and putative nucleocapsid (core) protein regions were highly conserved (99 % and 91% nucleotide identities, respectively). In contrast, the region immediately downstream which encodes a putative envelope glycoprotein(s) showed only 74% nucleotide identity between the two isolates. At the polypeptide level, the core and envelope domains showed 97% and 75% amino acid identities, respectively. This envelope variation may reflect the adaptation of HCV to the different hosts and/or the result of immunological selection. The highly conserved nucleotide sequence of the 5′ untranslated and core regions may play an important regulatory role in the life cycle of HCV.

DNA sequence analysis of the HindIII P region of a temperature-sensitive mutant of Autographa californica nuclear polyhedrosis virus confirmed the specific amplification of 1·4 kb of viral DNA from this region of the genome. The sequenced region included an open reading frame, translated in a counterclockwise direction, which would potentially encode a 74K protein. The amplified DNA was contained within this open reading frame, resulting in in-frame amplifications of a domain within the protein. Transcription studies revealed the presence of a ladder of viral RNA species corresponding to a 2·5 kb transcript carrying tandem repeats of about 1·4 kb. This indicated that the duplicated DNA was transcribed in the same orientation as the p10 gene. We predict that transcripts synthesized from the opposite DNA strand also consist of a ladder of related mRNAs which would be translated to produce a family of p74 proteins with multiple internal domains.

Primary bovine fibroblasts derived from foetal palate can be transformed by bovine papillomavirus type 4 DNA only in the presence of an activated ras gene, indicating that the virus does not encode all the information required for morphological transformation of non-established cells. A subgenomic fragment containing the complete E8 and E7 open reading frames (ORFs) induces transformation in cooperation with activated ras but transformation is abolished when the E7 ORF is deleted at the 3’ end, showing that this ORF encodes a necessary transforming function. Transformation is more aggressive when the E8 and E7 ORFs are placed under the transcriptional control of the long terminal repeat of the mouse Moloney leukaemia virus, suggesting that the degree of transformation is dependent on the level of expression of these genes.

The structural proteins of rubella virus (RV) are translated as a large polyprotein precursor, p110, which is processed to produce the mature virion components, the 33K capsid protein (C) and the two envelope glycoproteins, E1 (58K) and E2 (42K to 47K). The precise processing mechanism has not been elucidated; however it must include at least two proteolytic cleavages to release the individual virion components from the polyprotein, and it must provide for their dichotomous intracellular distribution. The C protein remains in the cytoplasm where it participates in the formation of nucleocapsids, while the envelope glycoproteins enter the cellular secretory pathway and are N-glycosylated and cleaved. Sequence analysis of the 24S mRNA encoding the polyprotein precursor suggests that both E1 and E2 are preceded by signal peptides for translocation across the membrane of the rough endoplasmic reticulum. A recent study has provided direct evidence that the putative signal peptide preceding E1 can in fact mediate translocation of E1. In this study, we have used in vitro translation- translocation assays to examine further the processing of RV glycoproteins. We have shown that the putative signal sequence preceding E2 can mediate translocation of the E2 protein in the absence of an intact E1 signal peptide. The experiments also revealed that cleavage of the E2-E1 polyprotein requires (i) the E2 signal peptide, (ii) microsomal membranes and (iii) sequences beyond the proximal half of the E1 signal peptide. Together these results suggest that separation of the E2 signal sequence as well as the proteolytic cleavage of El from E2 is performed by the cellular enzyme, signal peptidase.

Synthetic peptides representing amino acids 156 to 170 of virus capsid protein VP2 from human rhinovirus (HRV) type 2 have previously been used to elicit a neutralizing antibody response; polyclonal antisera against this peptide have been compared with a virusneutralizing monoclonal antibody (8F5) which recognizes the same linear sequence. The neutralizing activity of both antibodies against virus is abolished by an amino acid substitution in VP2 at position 163 but only the peptide antiserum neutralizing activity is affected by a change in VP2 at position 158. The minimal binding site of 8F5 has been mapped, using overlapping peptides, to a sequence TRLNPD covering VP2 residues 160 to 165. Using affinity purification it has been shown that 8 to 10% of total neutralizing activity of polyclonal rabbit or guinea-pig antivirus antiserum is due to recognition of this linear VP2 156 to 170 determinant. Furthermore, a similar population of neutralizing antibodies appears to be associated with an immune response to recent HRV infection in humans. These results confirm the existence of linear determinants on the surface of HRV which may be mimicked by suitable synthetic peptides.

Human placental trophoblast interferon (tro-IFN), induced in trophoblast cultures by a superinduction procedure, was purified to a homogeneous product with retention of biological activity. The problems associated with isolation from serum-containing medium were overcome by a combination of Blue Sepharose affinity chromatography and reversed-phase HPLC (RP-HPLC) on Separon SGX C-18. This two-step purification procedure yielded tro-IFN with a specific activity of 3·4 × 107 international units/mg of protein. The overall recovery of interferon activity was 66·7%. The purified tro-IFN was shown to be a glycoprotein with an Mr of 24K on native and SDS-PAGE. Its antiviral activity was stable at pH 2·0 at 37 °C but was sensitive to heat at 56 °C for 1 h and was neutralized by antibodies to human IFN-β.

Human term-placental trophoblasts in primary culture were studied for an interferon (IFN) response when challenged with Sendai virus and compared to three choriocarcinoma cell lines, placental fibroblasts and placental macrophages. Normal trophoblasts were high producers and released both IFN-α and IFN-β. In contrast, one choriocarcinoma cell line was a low producer and all malignant lines produced only IFN-β. Circulating monocytes produce IFN-α but placental macrophages secreted IFN-β and some IFN-α, suggesting that IFN production may be dependent on the stage of differentiation. A role for trophoblast IFNs in protection of the foetus against virus infections is proposed.

Persistent infections with several strains of mumps virus (strains Torii and Miyahara), measles virus (strains Edmonston, CAM-70, AIK-C and Schwarz) and subacute sclerosing panencephalitis (SSPE) virus (Hälle and Mantooth) were established in various cell lines (FL, KB, A549, SK-AS, 293, K562, Ramos and NC-37). Oligo-2′,5′-adenylate synthetase activity was demonstrated to be only slightly induced by interferon in cytoplasmic and nuclear fractions of cell lines persistently infected with mumps virus. In these cells, resistance to vesicular stomatitis virus infection was not induced by interferon treatment. Treatment of the persistently infected cells with interferon for 10 and 24 h did not stimulate an increase in the amount of synthetase mRNA. In cells persistently infected with measles and SSPE viruses, reduced induction of the enzyme varied with host cell types. Induction of the enzyme was not found in K562, SK-AS and KB cells, but was recognized in NC-37 and FL cells.

Extensive regions of heptad repeat units consistent with an α-helical coiled coil conformation are located adjacent to hydrophobic, potentially fusion-related regions in the amino acid sequences of paramyxovirus fusion and retrovirus envelope glycoproteins. Similar arrangements of hydrophobic peptides and heptad repeat units exist in coronavirus peplomer proteins and influenza virus haemagglutinins. This suggests that there may be similarities in the structures of these proteins and in the functions of the hydrophobic fusion-related regions during virus entry.

The complete nucleotide sequence of barley yellow mosaic virus (BaYMV) RNA 1 was obtained by analysis of overlapping cDNA clones and by direct RNA sequencing. The sequence is 7632 nucleotides in length, excluding a 3′ poly(A) tail. The first AUG codon at nucleotide 172 appeared to be the initiator for a single long open reading frame encoding a protein of 2410 amino acids with an Mr of 270755. Amino acid sequence comparisons revealed that the BaYMV 270K protein contains three regions upstream of the C- terminal capsid protein which share significant homologies with the cytoplasmic inclusion and two nuclear inclusion proteins of potyviruses thus indicating their similarities in genetic organization. However, the apparent low levels of homology in the corresponding proteins of BaYMV and potyviruses are in contrast with the high conservation among potyviruses. Moreover, our data indicate that BaYMV RNA 1 has no counterpart to the two cistrons located in the 5′- terminal region of the potyvirus genome. Although the data suggest a close evolutionary relationship between BaYMV and potyviruses, the striking differences set BaYMV apart from potyviruses.

Barley yellow dwarf virus (BYDV) can be separated into two groups based on, among other criteria, serological relationships that are presumably governed by the viral capsid structure. Nucleotide sequences for the coding regions of coat proteins of approximately 22 K were identified for the MAV-PS1, P-PAV (group 1) and NY-RPV (group 2) isolates of BYDV. The MAV-PS1 and P-PAV coat protein sequences shared 71 % deduced amino acid similarity whereas that of the NY-RPV isolate shared no more than 51 % similarity with either the MAV-PS1 or the P-PAV sequence. Other comparisons showed that these and other BYDV coat protein sequences examined to date share a high degree of identity with those identified from other luteoviruses. Among luteovirus coat protein sequences in general, several highly conserved domains were identified whereas other domains differentiate MAV- PS1 and PAV isolates from NY-RPV and other luteoviruses. Sequence similarities and differences among BYDV coat proteins (approx. 22K) are consistent with the serological relationships exhibited by these viruses. Amino acid sequence comparisons between BYDV isolates that share common aphid vectors indicate that it is unlikely that these coat proteins are involved in aphid specificity.

Twenty tomato spotted wilt virus (TSWV) isolates were serologically compared in ELISA employing five different procedures using a rabbit polyclonal antiserum against nucleocapsid proteins (NuAbR) and mouse monoclonal antibodies (MAbs), two directed to nucleocapsid proteins (N1 and N2) and four directed to glycoproteins G1 to G4. All the antisera were raised against TSWV-CNPH1. The 20 isolates were differentiated into two distinct serogroups. Serogroup I consisting of 16 isolates strongly reacted with NuAbR. The other four isolates were poorly recognized by NuAbR and were placed in another serogroup, designated II. The panel of MAbs differentiated the TSWV isolates into three serotypes. The 16 isolates forming serogroup I reacted strongly with the MAbs generated and were identified as serotype I isolates. The four isolates which made up serogroup II were split into serotypes II and III. The serotype II isolates did not respond or responded poorly with MAbs N1, N2 and G3. The two other isolates placed in serotype III were recognized by N1 but not by N2 and G3. Two isolates became defective after several mechanical passages and failed to respond or responded very poorly with MAbs directed to glycoproteins. Our results show that ELISA employing polyclonal and monoclonal antisera is a useful tool to differentiate TSWV isolates and to detect defective forms. The results also strongly suggest that TSWV nucleocapsid proteins are less conserved than the glycoproteins.

A panel of 15 mouse monoclonal antibodies (MAbs) was raised against five strains of alfalfa mosaic virus (AMV) which were closely related antigenically but biologically distinct. A wide diversity of MAb specificity was revealed by screening them in three formats of indirect ELISA, using native and glutaraldehyde- fixed AMV particles as well as isolated coat protein preparations. Of these MAbs, seven reacted specifically with only one AMV strain in at least one ELISA format and at least one MAb was capable of identifying each of the strains. One of the MAbs reacted with a cryptotope, whereas the other recognized different subtypes of either metatopes or neotopes, indicating that the AMV particle has a complex antigenic structure. Only two of the MAbs precipitated AMV in agarose gels. Another two, which recognized epitopes on coat protein subunits, also reacted well in immunoblots. One of the precipitating MAbs recognized an epitope which appears to be common to AMV and cucumber mosaic virus.

The 5′ and 3′ termini of four ssRNA species of rice stripe virus (RSV) isolate T were sequenced. The 3′ termini of the three smallest ssRNAs, i.e. RNAs 2, 3 and 4, had the sequence 5′ GACUUUGUGU 3′; that of ssRNA 1 had the sequence 5′ GACUAUGUGU 3′. The 5′-terminal sequences of all four ssRNAs were

5′ ACACAAAGUCC 3′. The 5′- and 3′-terminal sequences of about 20 bases of each ssRNA were almost complementary to each other. It is possible that RSV RNAs form panhandle structures characteristic of the RNA of negative-strand viruses.