The informosome-like virus-specific ribonucleoprotein (vRNP) may be involved in the transport of tobacco mosaic virus infection.

A new type of informosome-like virus-specific ribonucleoprotein (vRNP) differing from mature tobacco mosaic virus (TMV) particles in buoyant density and structure was found in TMV-infected cells (Yu. L. Dorokhov, N. M. Alexandrova, N. A. Miroshnichenko, and J. G. Atabekov, 1983, Virology 127, 237-252). Two groups of TMV ts mutants were used to discover whether there is a correlation between the vRNP formation and systemic spreading of virus infection (transport) over the infected plant. The first group of mutants (Ni118, flavum) contains a ts mutation in the coat protein gene but are capable of systemic spreading at nonpermissive temperature (tr transport); the second group of mutants (Ni2519, Ls1) cannot spread systemically at restrictive temperature (ts transport). It is shown that vRNP can be produced at restrictive temperature by tr-transport mutants but not by ts-transport mutants. The latter can produce vRNP only at a permissive temperature. The role of vRNP in long-distance transport of the virus infection is supported by two other observations: (a) upper leaves that were maintained at 5 degrees accumulate potentially infective material and material with the properties of vRNP but not virus particles and (b) plants that were simultaneously infected with Lsl and Ni118 at a non-permissive temperature exhibited long-distance transport and vRNP. These results also implicate coat protein in long-distance transport. It is suggested that vRNPs are novel types of virus-specific particles that are involved in both cell-to-cell and long-distance transport of TMV infections.