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Molecular Plant Pathology

The p27 Protein Is Present at One End of Citrus Tristeza Virus Particles. V. J. Febres, Plant Pathology Department, University of Florida, Gainesville 32611-0680. L. Ashoulin, M. Mawassi, A. Frank, M. Bar-Joseph, K. L. Manjunath, R. F. Lee, and C. L. Niblett. Eighth author: Plant Pathology Department, University of Florida, Gainesville 32611-0680; second, third, fourth, and fifth authors: The S. Tolkowsky Laboratory, Department of Virology, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel; and sixth and seventh authors: Citrus Research and Education Center, University of Florida, Lake Alfred 33850. Phytopathology 86:1331-1335. . Accepted for publication 9 September 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-1331.

Sequence analysis of the citrus tristeza closterovirus (CTV) genome indicated the presence of an open reading frame upstream of the capsid protein (CP) gene that codes for a protein of 27 kDa (p27). p27 is a diverged CP, showing 41% deduced amino acid sequence similarity with the CP. Previous reports indicated that CTV particles were composed of a single protein, the CP. However, adsorption of extracts of CTV-infected tissue to enzyme-linked immunosorbent assay (ELISA) plates with p27-specific antibodies and their detection with antibodies to the CP suggested that the p27 and CP were associated. The association of p27 with the virion was indicated by positive reverse transcription and polymerase chain reaction results using the p27-adsorbed material and two sets of primer pairs corresponding to the 5' and 3' ends of the CTV genome. Immunoelectron microscopy demonstrated that p27 antibodies decorated a 75- to 85-nm-long segment at one end of the virus particle, but not the main portion of the particle, for both a Florida and an Israeli strain of CTV. Conversely, the CP antibodies decorated the majority of the virus particle, but not a terminal 75- to 85-nm-long segment. Both normal length (about 2,000 nm) and shorter particles contained the p27 segment.