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Mouse monoclonal antibodies (MAbs) against the Australian B strain of clover yellow vein (C1YVV-B) and the JG strain of Johnsongrass mosaic (JGMV) potyviruses were produced, characterised and the epitopes with which they reacted were deduced. Using intact particles of C1YVV a total of ten MAbs were obtained which reacted strongly with C1YVV-B in an enzyme-linked immunosorbent assay and Western blots. Four of these MAbs (1, 2, 4, and 13) were found to be ClYVV-specific, as they reacted with all five C1YVV strains from Australia and the U.S.A. but not with 11 strains of bean yellow mosaic (BYMV), pea mosaic (PMV), and white lupin mosaic (WLMV) viruses which, together with C1YVV, form the BYMV subgroup of potyviruses. These MAbs failed to react with eight other potyvirus species, including six which infect legumes like the viruses in the BYMV subgroup. The C1YVV MAb 10 was found to be BYMV subgroup-specific. It reacted strongly with 15 of the 16 strains of viruses in the subgroup and gave no reaction with eight other potyviruses. The other five C1YVV MAbs reacted with varying degrees of specificity with the BYMV subgroup viruses and also with other potyviruses. Eight of the C1YVV MAbs (1, 2, 4, 5, 13, 17, 21, and 22) reacted with the intact coat proteins only and not with the truncated (minus amino terminus) coat protein of C1YVV suggesting that the epitopes for these MAbs are located in the surface-exposed, amino-terminal region of the C1YVV coat protein. Comparison of published coat protein sequences of BYMV and C1YVV isolates indicated that the epitopes for the four ClYVV-specific MAbs may be in the amino-terminal region spanning amino acid residues 18 to 30, whereas those for the other four MAbs may be located in the first 17 amino-terminal amino acid residue region. The epitopes that reacted with BYMV subgroup-specific MAb 10 and MAb 30 which reacted with 20 of the 24 potyvirus isolates, are probably located in the core region of C1YVV coat protein as these MAbs reacted with the intact as well as truncated coat protein of C1YVV. Analysis, in Western blot immunoassay, of 17 MAbs raised against virions of JGMV revealed that only two MAbs (1–25 and 4–30) were JGMV-specific, whereas others displayed varying degrees of specificity to different potyviruses. When these MAbs were screened against the intact and truncated (minus 67 amino-terminal amino acid residues) coat proteins of JGMV, the two JGMV-specific MAbs reacted only with the intact coat protein, whereas the other MAbs reacted with the intact as well as with truncated coat proteins, in Western blots. These results suggest that the epitopes for the two JGMV-specific MAbs are located in the surface-exposed amino-terminal 67 amino acid residue region and those for the cross-reactive MAbs are contained in the conserved core region of the JGMV coat protein. Screening of potyvirus MAbs against intact and truncated coat proteins thus appears to be a simple procedure to select virus-specific MAbs to potyviruses.

The 1,035 nucleotides at the 3'end of the I strain of pea mosaic potyvirus (PMV-I) genomic RNA, encoding the coat protein, have been cloned and sequenced. A comparison of the derived coat protein sequence with those of the bean yellow mosaic virus (BYMV) strains, CS, S, D and GDD, indicates that PMV-I is a strain of BYMV. Sequence comparisons and hybridisation studies using the 3'-noncoding region support this classification. The nucleotide and protein sequence data also suggest that PMV-I and BYMV-CS form one subset of BYMV strains while the other three strains form another.

The N-terminal region of the coat proteins of five strains (Isis, Brisbane, Sabi, Bundaberg, and BC) of sugarcane mosaic virus (SCMV) isolated from four different plant species (sugarcane, sabi grass, wild sorghum, and blue couch grass) have been compared with the previously published data for SCMV-SC and SCMV-MDB, isolated from sugarcane and maize, respectively. The region, beginning at residue 11 and ending 16 residues beyond the second trypsin cleavage site of the coat protein, varied in size from 68 amino acid residues (Bundaberg) to 115 residues (BC) and contained repeat sequence motifs. Comparisons of the sequence identity and the nature of the repeats in the seven sequences showed that there were five different sequence patterns. These could be grouped further into three subsets which appeared to correlate with the host range of the strains. SCMV-Brisbane, SC, and Isis, isolated from sugarcane, showed almost identical sequence patterns and formed one subset. The other four strains had different sequence patterns and could be grouped further into a Sabi and Bundaberg subset (isolated from sabi grass), and a BC and MDB subset.

The taxonomic relationships of 20 potyvirus isolates from the bean yellow mosaic virus (BYMV) subgroup were investigated by high-performance liquid chromatographic peptide profiling of tryptic digests of their coat proteins. The peptide profiles of the clover yellow vein virus (CIYVV) strains B, C81, LI, and Washington were almost identical to each other and were closely related to that of CIYVV-Pratt, confirming their status as strains of CIYVV and not strains of BYMV. The profiles of BYMV-GDD, G, WA8, WA22, and RL7 were almost superimposable on each other and were similar to the profiles of BYMV-Scott, S, G81, and F, indicating that their coat proteins were very similar []