ANTIGENIC ANALYSIS OF POTATO VIRUS-A PARTICLES AND COAT PROTEIN

Five monoclonal antibodies (MAbs) were prepared to particles of potato virus A (PVA), isolate B11. In immunoblots, MAbs A1D8 and A5B6 reacte d only with full length molecules of PVA coat protein (CP). Pepscan te sts with overlapping octapeptides representing the whole sequence of P VA CP showed that the epitope detected by MAb A5B6 is contained in its N-terminal octapeptide. MAbs A9A4, A3H4 and A6B8 reacted with CP mole cules that lacked about 5 kD of sequence at their end(s) and detected epitopes at residues 52 to 62, 64 to 73 and 75 to 82 respectively, all of which lie in the protease-resistant core of the CP. The epitope wh ich reacts with MAb A3H4 is in a region predicted to be hydrophobic an d is not detected in intact virus particles, indicating it is a crypto tope. In contrast, MAbs A6B8 and A9A4 reacted with freshly purified PV A particles but more strongly with partially degraded ones. Pepscan te sts with polyclonal antibodies to PVA isolate B11 identified five addi tional immunogenic sequences in PVA CP and showed that regions at the N-termini of the intact and core molecules are immunodominant. PVA iso late B11 was not transmitted by aphids, and its CP N-terminal octapept ide contains the sequence DAS, which is associated with aphid-non-tran smissibility in other potyviruses. MAb A5B6, which detects this region , reacted strongly in ELISA with three out of four other aphid-non-tra nsmissible PVA isolates but only weakly with three aphid-transmissible ones, suggesting that differences in N-terminal sequence may underlie most of the differences in aphid transmissibility.