title: Functions of the 126- and 183-kDa proteins of tobacco mosaic virus.
abstract: Tobacco mosaic virus produces two proteins that contain domains similar to the methyltransferase (MT) and helicase (HEL)-like domains of the replicase-associated proteins of other RNA viruses. The more abundant 126-kDa protein contains only the MT and HEL-like domains, whereas the 183-kDa readthrough protein additionally contains the polymerase domain. We examined the functions of these proteins by constructing a bipartite system to express the 126- and 183-kDa proteins from separate RNAs. Mutants expressing the 183-kDa protein recognized promoters for negative- and positive-stranded RNA synthesis, transcribed subgenomic mRNAs, capped RNAs, synthesized proteins, moved cell to cell within the plant, and replicated defective RNAs (dRNAs). The principal function of the 126-kDa protein was to increase the rate of replication approximately tenfold. The 126-kDa protein appeared to function primarily in cis, and production of the 126-kDa protein in trans did not enhance replication of the helper virus. dRNAs producing a functional 126-kDa protein were replicated efficiently by helper viruses that produced only the 183-kDa protein but not by wild-type virus, suggesting that efficient replication required the 183-kDa protein to form a heterodimer with the 126-kDa protein already bound to the target dRNA.
authors.affiliation: Department of Plant Pathology, University of Florida, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, Florida 33850, USA. djlew@lal.ufl.edu
authors.forename: D J
authors.initials: DJ
authors.lastname: Lewandowski
authors.forename: W O
authors.initials: WO
authors.lastname: Dawson
mesh_terms: D016368:Frameshift Mutation; D015967:Gene Expression Regulation, Viral; D008970:Molecular Weight; D053830:Plant Viral Movement Proteins; D010947:Plants, Toxic; D012324:RNA-Dependent RNA Polymerase / Q000502:physiology*; D014026:Nicotiana / Q000821:virology; D014027:Tobacco Mosaic Virus / Q000235:genetics / Q000502:physiology*; D014764:Viral Proteins / Q000378:metabolism / Q000502:physiology*; D014779:Virus Replication
chemical_list: C071899:130k protein, Tobacco mosaic virus; D053830:Plant Viral Movement Proteins; D014764:Viral Proteins; C085103:tobacco mosaic virus replicase; D012324:RNA-Dependent RNA Polymerase