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The sequences of the 5′ terminal 1140 and 3′ terminal 1546 nt of tomato ringspot virus (TomRSV) RNA1 have been determined. These sequences share a high degree of nucleotide sequence similarity with the previously determined TomRSV RNA2 sequence. Eighty-eight percent of the 5' terminal 907 nt of TomRSV RNA1 and RNA2 contain identical nucleotide residues; the first 459 nt are identical at all positions, whereas the next 447 nt are identical at only 75.8% of the nucleotide positions. The region of similarity includes not only the 5' nontranslated leader but also sequence probably encoding polyproteins. The 3′ terminal 1533 nt of TomRSV RNA1 and RNA2 are identical and are noncoding. The sequences common to RNA1 and RNA2 account for almost 35% of the total genomic sequence. It is possible that the similar sequences at both ends of TomRSV RNA1 and RNA2 are a result of recombination between these two genomic RNA components.

The coat protein gene from potato virus S (PVS) was introduced into Nicotiana debneyii by leaf disc transformation using Agrobacterium tumefaciens. Transgenic plants expressing the viral coat protein were highly resistant to subsequent infection by the ME strain of PVS as indicated by an absence of symptom development and a lack of accumulation of virus in both the inoculated and upper leaves. As in reported experiments with plants expressing potato virus X coat protein, plants expressing PVS coat protein were also protected from inoculation with PVS RNA. These results provide further evidence that coat protein-mediated protection for these two groups of viruses, which share similar genome organizations, may involve inhibition of some early event in infection other than or in addition to virus uncoating.

The sequence of tomato ringspot virus (TomRSV) RNA-2 has been determined. It is 7273 nucleotides in length excluding the 3′ poly(A) tail and contains a single long open reading frame (ORF) of 5646 nucleotides in the positive sense beginning at position 78 and terminating at position 5723. A second in-frame AUG at position 441 is in a more favourable context for initiation of translation and may act as a site for initiation of translation. The TomRSV RNA-2 3′ non-coding region is 1550 nucleotides in length. The coat protein is located in the C-terminal region of the large polypeptide and shows significant but limited amino acid sequence similarity to the putative coat proteins of the nepoviruses tomato black ring (TBRV), Hungarian grapevine chrome mosaic (GCMV) and grapevine fanleaf (GFLV). Comparisons of the coding and non-coding regions of TomRSV RNA-2 and the RNA components of TBRV, GCMV, GFLV and the comovirus cowpea mosaic virus revealed significant similarity for over 300 amino acids between the coding region immediately to the N-terminal side of the putative coat proteins of TomRSV and GFLV; very little similarity could be detected among the non-coding regions of TomRSV and any of these viruses.

Summary The sequence of 3553 nucleotides corresponding to the 3′-terminal region of potato virus S (PVS) has been determined from cloned cDNA. The sequence obtained contains six open reading frames (ORFs) encoding proteins of M r 10734, M r 32515, M r 7222, M r 11802, M r 25092 and at least M r 41052. The sequence of the 33K ORF has been confirmed to be that of the viral coat protein gene. The nucleotide sequence of this ORF was obtained from plasmids which were isolated by colony hybridization with a specific monoclonal antibody to PVS, and the expression of coat protein fusion products was verified by Western blots of bacterial cell lystates. The deduced amino acid sequence of a 70 amino acid portion from the central region of the PVS coat protein was 59% identical to the analogous region of potato virus X. In addition, the 7K, 12K and 25K ORFs displayed significant sequence homology with the similarly sized ORFs from a number of potexviruses. The partial 41K ORF product was homologous with the C-terminal portion of the viral replicase proteins of potato virus X and white clover mosaic virus.

Summary Four isolates of carnation ringspot virus showed a reversible aggregation which was dependent on the temperature and concentration of their preparations. At 7 mg/ml, preparations of two of these isolates aggregated at room temperature but at the same concentration the other two isolates required higher temperatures (40 °C) for aggregation. A fifth isolate formed aggregates of 12 virus particles and linked aggregates. Particles of the two isolates with less tendency to aggregate were almost completely dissociated by 0.4% sodium dodecyl sulphate (SDS) at pH 5 and by 0.1% SDS at pH 7. At pH 7, an RNA component of mol. wt. 0.5 × 106 was released by lower concentrations of SDS than was an RNA component of 1.5 × 106. At pH 5, the sedimentation rates of unaggregated particles of the remaining three aggregating strains were unaffected by up to 15% SDS. However, treatment with 0.0075 to 0.05% SDS at pH 7 produced protein, RNA and swollen virus particles. These swollen particles were not further affected by increasing the SDS concentration to 8%.

Summary The N-terminal cyanogen bromide peptide of the coat protein of the cowpea strain of southern bean mosaic virus (SBMV-C) was purified by high-pressure liquid chromatography and used as an immunogen in the production of monoclonal antibodies. One monoclonal antibody, designated 4D6, bound to both purified peptide and immobilized virus in a solid-phase ELISA. The reactivity of this monoclonal antibody with immobilized peptide could not be inhibited by native SBMV-C but was inhibited by low levels of EDTA-swollen virus in an antigen inhibition ELISA. The binding of 4D6 to the swollen conformation of the virus was not significantly diminished upon collapsing the swollen virus by pH adjustment or addition of calcium ions. Reactivity of the antibody was also observed with native virus particles which had been dialysed against weakly alkaline buffers. The binding of 4D6 was extremely sensitive to trypsin proteolysis of the virus coat protein, indicating that the antibody binding site was most likely located within the first 30 amino acid residues of the N-terminus. Monoclonal antibody 4D6 also cross-reacted weakly with red clover necrotic mosaic virus in both indirect ELISA and antigen inhibition ELISA.

Summary Cloned DNA representing the sequence coding for the non-structural protein 3A from cucumber mosaic virus (CMV) was inserted in an expression vector containing a truncated portion of the Protein A gene from Staphylococcus aureus. Expressed fusion protein was purified from Escherichia coli cell extracts by affinity chromatography on rabbit gamma globulin-conjugated Sepharose and used as an immunogen for the production of monoclonal antibodies (MAbs). Five MAbs that reacted with pXCM3A13 fusion protein in solid phase ELISA were able to immunoprecipitate specifically protein 3A from mixtures of in vitro translation products of CMV RNA. None of these antibodies reacted with the analogous protein in translation products of brome mosaic virus RNA, but all of them reacted with the 3A protein from tomato aspermy virus. Immunogold labelling of ultrathin sections of CMV-infected tobacco tissue with MAb 3H12 demonstrated that the 3A protein accumulated within the nucleoli of these cells. This location differs from that of the analogous 3A protein of alfalfa mosaic virus which is associated with the middle lamella of the cell walls of infected tobacco cells.

Summary Double-stranded cDNA copies of RNA-1 and RNA-2 of tomato ringspot virus were cloned into pUC9. Comparison of restriction enzyme maps of eight clones indicated that 1.9 kb at the 3′ termini of RNA-1 and RNA-2 were similar. Five of these clones were used in Northern hybridization analyses and found to contain sequences either unique to RNA-1 or RNA-2, or common to RNA-1 and RNA-2. Southern blot analyses using clones derived from RNA-1 and RNA-2 confirmed that there is a 1.9 kb nucleotide sequence homology at the 3′ termini. A sequence homology of this magnitude has not been reported previously for other plant viruses with multipartite ssRNA genomes.

Summary The amino acid composition, behaviour in SDS-polyacrylamide gel electrophoresis and electrophoretic patterns of cyanogen bromide peptides were studied for the protein subunits of different preparations of potato virus X (PVX). The results indicate that the protein subunits of PVX can be partially degraded in the intact virus at the N-terminus by reducing agent-dependent proteases in crude plant sap and by trypsin, and at the C-terminus by reducing agent-independent proteases occurring in some virus preparations.

1. Vitamin requirements for growth and sporulation of Saccharomyces cerevisiae were compared, using a chemically controlled presporulation medium and 0.1% sodium acetate solution as the sporulation medium. The six vitamins added to the media, singly or in combination, were those frequently found to be required for the growth of yeast: biotin (B), calcium pantothenate (P), inositol (I), niacin (N), pyridoxine hydrochloride (Py), and thiamin hydrochloride (T). 2. For growth B and P were required, although the initial need for the latter was slowly overcome. 3. Cells cultured on the basal medium plus vitamins did not require vitamins in the sporulation medium for sporulation; however, addition of P, but not B, to the latter moderately increased ascus yields. 4. The vitamin content of the presporulation medium largely determined yields of asci in the sporulation medium; these yields were low without B in the former medium. The concentration of B required seemed higher for maximum sporulation than for optimum ...

Summary Complementary DNA copies of the genomic RNA of melon necrotic spot virus (MNSV) have been cloned and the region deduced to encode the coat protein has been sequenced. The putative coat protein coding region, located near the 3′ end of the genome, consists of 1170 nucleotides and has the potential to encode a 390 amino acid protein of M r 41840. Our data show that although MNSV is a carmovirus, its coat protein more closely resembles those of the tombusviruses than those of the carmoviruses sequenced to date, in both the extent of sequence similarity and in the length of the random/arm and protruding domains of the coat protein. Furthermore, dot matrix comparisons revealed sequence similarity between the coat protein protruding domains of MNSV and the cucumber necrosis tombusvirus. This similarity may be involved in one or more of the biological properties these two viruses share, such as the ability to infect cucumbers naturally and to be transmitted by the soil-inhabiting fungus Olpidium radicale.

Summary Antibodies induced by the injection of alfalfa mosaic virus (AMV) or the protein of turnip crinkle virus (TCV) reacted with the viruses and their respective protein subunits in gel-diffusion tests. The ratios of virus-reactive antibodies to protein-reactive antibodies were different in two fractions obtained by chromatography of the sera on DEAE-Sephadex. The first DEAE-Sephadex fraction contained a greater proportion of virus-reactive antibodies than did the second fraction or the unfractionated antiserum. Electrophoretic mobility measurements at pH 8.6 showed that AMV and TCV had a greater negative charge per unit surface area than did their respective proteins.

The molecular weight of Tipula iridescent virus, based on sedimentation and diffusion coefficients, was 5.51 × 10 8 , with hydration of 0.57 g of water per g of virus. Deoxyribonucleic acid content, based on total inorganic phosphorus liberated, was 19 ± 0.2%. At 260 mμ, the virus gave an uncorrected absorbance of 18.2 cm 2 /mg of virus and a light-scattering corrected absorbance of 9.8 cm 2 /mg of virus. Amino acid analyses of the virus protein revealed a remarkable similarity to Sericesthis iridescent virus. The possibility is discussed that the four iridescent insect viruses reported to date bear a strain relationship.

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