SUMMARYThe 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 Mr 10 734, Mr 32 515, Mr 7222, Mr 11 802, Mr 25092 and at least Mr 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.

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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.

SUMMARYComplementary 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 Mr 41 840. 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.

SUMMARYThe 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.

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SUMMARYThe electrophoretic patterns of dsRNA species isolated from cucumber plants infected with cucumber necrosis virus (CNV) and from Nicotiana clevelandii plants infected with tomato bushy stunt virus (TBSV) were almost identical and differed greatly from the electrophoretic patterns of dsRNA species isolated from tobacco plants infected with tobacco necrosis virus (TNV). Hybridization with cloned cDNA of CNV showed that there was extensive homology between the nucleic acids of CNV and TBSV but not between those of CNV and TNV. Gel diffusion tests and ELISAs showed no serological relationship between CNV and five tombusviruses. TBSVinfected N. clevelandii plants showed some cross-protection against infection by CNV but not against infection by carnation ringspot virus. CNV therefore resembles TBSV more than TNV and should be classified as a tombusvirus.