SUMMARYA procedure is described for purifying the bl, b2 and b3 proteins from leaves of Nieotiana tabacum cv. Xanthi-nc, a cultivar reacting hypersensitively to tobacco mosaic virus (TMV). All three proteins consist of a single polypeptide, have similar mol. wt. of about ]4 2oo but differ in charge. In contrast, the b4 protein differs from bl to b3 in both charge and size. The same procedure purifies the proteins IV, III and II from TMV-infected leaves of N. tabacum cv. Samsun NN. The Samsun NN proteins IV to II resemble the bl to b3 proteins from Xanthi-nc in electrophoretic mobility in polyacrylamide gels and in mol. wt. ; b~, IV and III have similar amino acid compositions.It is suggested that these proteins be called pathogenesis-related proteins (PRs) and a unified system of nomenclature is proposed which groups similar proteins.

The complete nucleotide sequence of a virus infecting winter wheat in Shandong province, China has been determined. This was previously thought to be soil-borne wheat mosaic virus but, while the two viruses are related, they are only 75 % (RNA1) and 63 % (RNA2) identical at the nucleotide level, while the amino acid sequences share from 62 % (19 kDa RNA2 product) to 84 % (RNA1 replicase) identity. The analysis shows that the Chinese virus should be considered a new member of the genus Furovirus and has been named Chinese wheat mosaic virus (CWMV). A Cys-Gly … CysGly-X-X-His amino acid pattern was identified in the cysteine-rich protein of CWMV and those of several other plant virus genera, which seems likely to have some functional significance.

The new plant virus family Flexiviridae is described. The family is named because its members have flexuous virions and it includes the existing genera Allexivirus, Capillovirus, Carlavirus, Foveavirus, Potexvirus, Trichovirus and Vitivirus, plus the new genus Mandarivirus together with some related viruses not assigned to any genus. The family is justified from phylogenetic analyses of the polymerase and coat protein (CP) sequences. To help to define suitable molecular criteria for demarcation of species, a complete set of pairwise comparisons was made using the nucleotide (nt) and amino acid (aa) sequences of each fully-sequenced gene from every available accession in the family. Based on the distributions and on inspection of the data, it was concluded that, as a general rule, distinct species have less than ca. 72% identical nt or 80% identical aa between their entire CP or replication protein genes.

Degenerate primers for RT-PCR were designed and used to amplify genome fragments ( c. 750 nt in the coat protein-ORF6 region) of allexiviruses from a total of 28 garlic samples from 24 provinces in China. Many samples contained more than one distinct sequence. A total of 60 different sequences were obtained. Phylogenetic analysis and two-way comparisons were used to assess the status of the sequences and to re-examine the criteria for distinguishing species within the genus. Most of the sequences could be allocated to either Garlic virus D or Garlic virus X on the basis of sequence similarity but some appeared to be intermediate between existing species. There were no sequences of Garlic virus C or Shallot virus X. A comparison with the related genera Carlavirus, Foveavirus and Potexvirus suggests that the published allexivirus species demarcation criteria may have been drawn too tightly and should be re-examined.

At a concentration of 0.4 μg purified pokeweed antiviral protein (PAP)/ml, the formation of local lesions on tobacco leaves caused by tobacco mosaic virus infection was completely inhibited and at 25 ng PAP/ ml. 68% inhibition was still obtained. PAP protected plants from infection by viruses from seven virus groups‐five RNA viruses: tobacco mosaic virus, cucumber mosaic virus, alfalfa mosaic virus, potato virus X and potato virus Y; and two DNA viruses: African cassava mosaic virus (ssDNA) and cauliflower mosaic virus (dsDNA). Virus infection was probably blocked by PAP at a very early stage. PAP infiltrated into the intercellular spaces through the lower surfaces of leaves inhibited infection by virus inoculated on the upper leaf surface, and partially prevented PVY transmission by aphids. However. PAP did not show any activity against two bacterial and six fungal pathogens.