EVIDENCE THAT A VIRAL REPLICASE PROTEIN IS INVOLVED IN THE DISASSEMBLY OF TOBACCO MOSAIC-VIRUS PARTICLES IN-VIVO

Tobacco mosaic virus (TMV) particles have been shown to undergo bidire ctional disassembly when they are introduced into host cells. Approxim ately three-quarters of the genomic RNA (i.e., the 126-kDa and 183-kDa protein ORFs) is first uncoated in the 5'-to-3' direction and the pro cess is then completed by removal of coat protein molecules in the 3'- to-5' direction. An effort was made to determine whether the 126-kDa p rotein or the 183-kDa protein, both of which are involved in replicati on of the viral RNA, is required for the second part of the disassembl y reaction. It was shown that progeny negative-strand viral RNA begins to be produced in inoculated cells at about the same time that 3'-to- 5' disassembly is initiated thus suggesting that the two processes may be coupled. Particles containing mutant forms of the viral RNA in whi ch large sections of the 126-kDa and 183-kDa protein ORFs were missing were not disassembled in the 3'-to-5' direction when they were introd uced into cells. However, they were disassembled when the inoculum con tained purified TMV RNA from which, presumably, the two functional pro teins could be translated. Particles containing mutants of the RNA fro m which a few codons had been deleted in or near conserved regions in the 126-kDa protein ORF also did not undergo 3'-to-5' disassembly unle ss mixed with wild type viral RNA prior to inoculation. These results suggest that the 126-kDa and/or 183-kDa protein plays a role in the co mpletion of disassembly of TMV particles at the onset of the infection process. (C) 1997 Academic Press.