- Volume 70, Issue 5, 1989

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.

Several strains of cucumber mosaic virus (CMV) have been classified, and nucleic acid hybridization data indicate that these strains differ widely in nucleotide sequence. We have constructed cDNA clones of the coat protein coding regions of CMV strains C and WL, and have compared the nucleotide sequences of the RNA 3 intergenic region, coat protein gene, and 3′ untranslated region with published CMV sequences from the same regions of the Q, D and Y strains. These comparisons show that the C and WL strains belong to different CMV subgroups, and that the subgroups are more closely related in sequence than suggested by previous nucleic acid hybridization studies.

The bipartite genome of pea enation mosaic virus (PEMV) is often accompanied by a non-essential third RNA (M r 0·3 × 106) of unknown origin and function. Although the Wisconsin strains of PEMV originally lacked this RNA, we have monitored the appearance of a putative replicative form of this species in PEMV-infected tissue. In later generations encapsidated single-stranded RNA 3 appeared. We have used a 750 bp clone generated against the ds replicative form of RNA 3 to probe viral and host-derived nucleic acids to establish the relationship of this RNA to PEMV infection. Northern blot analysis showed that RNA 3 is distinct from viral genomic RNA and from host RNA. Similarly, Southern blot analysis showed that RNA 3 is distinct from the host genome. Infectivity analysis of fractionated viral RNAs coupled with Northern blot analysis confirmed that RNA 3 is both non-essential for PEMV infection, and non-infectious when inoculated on its own. RNA 3 does not influence symptom expression, aphid transmission or particle morphology. We conclude that RNA 3 of PEMV is a satellite RNA.

Monoclonal antibodies (MAbs) were prepared against the cylindrical inclusion protein (CIP), amorphous inclusion protein (AIP) and capsid protein (CP) of watermelon mosaic virus 2 (WMV2). Using the MAbs, CIP, AIP and CP were detected, roughly quantitatively, in WMV2-infected pumpkin leaves showing various symptoms by using electroblot-ELISA. From symptomless leaves and most dark green areas in the mosaic pattern no protein or small amounts of the three proteins were detected, but from most yellow areas in the mosaic almost equal amounts of each protein were detected in abundance. Leaves showing mild vein-yellowing and vein-clearing (respectively, the first and second leaves of the plants tested) contained AIP and CP in large amounts, but little CIP. On the other hand, expanding leaves contained CIP and AIP in large quantities, butCP in traces only. Therefore the distributions of CIP, AIP and CP in pumpkin plants were very uneven, but correlated with symptoms. In addition, the ratio of the concentrations of CIP, AIP and CP varied from tissue to tissue.

Mouse monoclonal antibodies (MAbs) were prepared to an inhibitor of virus replication (IVR), released from protoplasts or leaf tissue of hypersensitive tobacco plants infected with tobacco mosaic virus. The MAbs were highly specific for IVR and reduced its antiviral activity. Using these MAbs in affinity chromatography enabled the recovery of purified IVR. SDS-PAGE of the immunoaffinity-purified IVR gave a single M r 23K band. Immunoblots of IVR from extracts of protoplast or leaf tissue also revealed a single M r 23K band which suggests that protoplast and tissue IVR are closely related.

The complete nucleotide sequence of the phytoreovirus rice dwarf virus (RDV) genome segment 9 is presented. It consisted of 1305 nucleotides and had an open reading frame that codes for a putative polypeptide of 351 amino acids. M r of the protein was calculated to be 38 598. The terminal nucleotides 5′ GGUAAA--GAU 3′ were the same as those of RDV genome segment 10. The fourth nucleotide from the 3′end of an expected conserved sequence was a C rather than the U found in the previously sequenced genome segment 10. A structure similar to the segment-specific inverted repeat of wound tumour virus was also found in the terminal region of segment 9.