MONOCLONAL-ANTIBODIES DETECT A SINGLE AMINO-ACID DIFFERENCE BETWEEN THE COAT PROTEINS OF SOILBORNE WHEAT MOSAIC-VIRUS ISOLATES - IMPLICATIONS FOR VIRUS STRUCTURE

Four monoclonal antibodies (MAbs) were prepared against an isolate of soilborne wheat mosaic furovirus from Oklahoma (SBWMV Okl-7). Three MA bs had different reactivities in tests on SBWMV isolates from Nebraska (Lab1), France, and Japan. One MAb (SCR 133) also reacted with oat go lden stripe furovirus. None of the MAbs cross-reacted with other rod-s haped viruses including beet necrotic yellow vein furovirus, potato mo p-top furovirus, and tobacco rattle tobravirus. Sequence analysis of n ucleotides between 334 and 1,000 of RNA 2, the region that encodes the coat protein (CP) and the first 44 amino acids of a readthrough prote in, of the four SBWMV isolates revealed up to 27 base changes from the published sequence of a Nebraska field isolate of SBWMV. Most changes were translationally silent, but some caused differences of one to th ree amino acids in residues located near either the N- or C-terminus o f the CPs of the different isolates. Two further single amino acid cha nges were found at the beginning of the readthrough domain of the CP-r eadthrough protein. Some of these amino acid changes could be discrimi nated by MAbs SCR 132, SCR 133, and SCR 134. Peptide scanning (Pepscan ) analysis indicated that the epitope recognized by SCR 134 is located near the N-terminus of the CP. SCR 132 was deduced to react with a di scontinuous CP epitope near the C-terminus, and SCR 133 reacted with a surface-located continuous epitope also near the C-terminus. Predicti ons of CP structure from computer-assisted three-dimensional model bui lding, by comparison with the X-ray fiber diffraction structure of tob acco mosaic virus, suggested that the three CP amino acids found to di ffer between isolates of SBWMV were located near the viral surface and were in regions predicted to be antigenic.