Rice tungro bacilliform virus open reading frame 3 encodes a single 37-kDacoat protein

Rice tungro bacilliform virus (RTBV) is a plant pararetrovirus and a member of the Caulimoviridae family and closely related to viruses in the Badnavi rus genus. The coat protein of RTBV is part of the large polyprotein encode d by open reading frame 3 (ORF3). ORF3 of an RTBV isolate from Malaysia was sequenced (accession no. AF076470) and compared with published sequences f or the region that encodes the coat protein or proteins. Molecular mass of virion proteins was determined by mass spectrometry (matrix-assisted laser desorption/ionization-TOF) performed on purified virus particles from three RTBV isolates from Malaysia. The N- and C-terminal amino acid sequences of the coat protein were deduced from the mass spectral analysis, leading to the conclusion that purified Virions contain a single coat protein of 37 kD a. The location of the coat protein domain in ORF3 was reinforced as a resu lt of immunodetection reactions using antibodies raised against six differe nt segments of ORF3 using Western immunoblots after SDS-PAGE and isoelectro focusing of proteins purified from RTBV particles. These studies demonstrat e that RTBV coat protein is released from the polyprotein as a single coat protein of 37 kDa. (C) 1999 Academic Press.