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Mapping of Epitopes for Citrus Tristeza Virus-Specific Monoclonal Antibodies Using Bacterially Expressed Coat Protein Fragments. Olga V. Nikolaeva, Citrus Research and Education Center, University of Florida, 700 Experiment Station Road, Lake Alfred 33850-2299; Alexander V. Karasev(2), Charles A. Powell(3), David J. Gumpf(4), Stephen M. Garnsey(5), and Richard F. Lee(6). (2)(6)Citrus Research and Education Center, University of Florida, 700 Experiment Station Road, Lake Alfred 33850-2299; (3)Indian River Research and Education Center, University of Florida, Fort Pierce 34945; (4)Department of Plant Pathology, University of California, Riverside 92521; (5)USDA-ARS Horticultural Research Laboratory, 2120 Camden Road, Orlando, FL 32803. Phytopathology 86:974-979. Accepted for publication 10 June 1996. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1996. DOI: 10.1094/Phyto-86-974.

Epitopes for a panel of 30 monoclonal antibodies (MAbs) specific for citrus tristeza virus (CTV) were mapped on the CTV coat protein (CP) expressed in bacterial cells. Expression constructs that generated different portions of the CTV CP were screened against MAbs by Western blotting and enzyme-linked immunosorbent assay. All MAbs analyzed could be placed into five groups (I to V), four of which have continuous sequential epitopes. Group I has an epitope within the nine C-terminal amino acids (aa), 215 to 223, that reacted only to MAb 4H6; the group II epitope was mapped between aa 173 and 215 and reacted to MCA-14; the group III epitope was mapped between aa 118 and 128 and reacted to five MAbs, including MCA-13; and the group IV epitope was mapped between aa 2 and 121 and reacted to four MAbs. Epitope(s) for a large group of MAbs (group V) either were conformational or included a conformational element, because they only reacted with the complete CP fusion protein and not with its fragments. Specific proteolytic cleavage of a CP fusion protein expressed in Escherichia coli as a peptide fused to a maltose-binding protein (MBP) released a full-size CP with essentially no reactivity with MAbs from group V. Additional studies will be needed to differentiate members of this group. The linear, continuous epitope for MCA-13 (aa 118 to 128), which distinguishes Florida quick decline-inducing (D-I) CTV isolates from mild isolates, was expressed in E. coli cells as a peptide fused to an MBP. This fusion protein was purified and used as antigen to generate a rabbit polyclonal antiserum. The aa 118 to 128-specific polyclonal antiserum had the same serological properties as MAb MCA-13 and reacted with Florida quick D-I CTV isolates but not with mild isolates.