Tobravirus Group - Tobacco Rattle Virus TRV

Tobravirus Group - Tobacco Rattle Virus TRV

	Tobravirus Group - Tobacco Rattle Virus (TRV) These are rigid rod shaped ssRNA viruses with a divided genome. Several strains have been distinguished. Each strain contains two or three types of particles of different lengths. All strains have long particles (L) 188-197 nm in length and short particles (S) (43-114nm), the number and size of which depend upon the nature of the strain. The PRN strain contains 75 nm short particles, and the CAM strain 52 nm particles. The B strain contains two short particles 50 and 110 nm in length and the C strain 50 and 85 nm short particles.
Stable Tobacco rattle virus production occurs only when both Land S particles are present in the inoculum. The L particle RNA can replicate itself, but lacks the information to code for coat protein. It presumably codes for replicase which is necessary for the replication of RNA of L and S-particles. The S particle contains the information for coat protein and replication, but cannot replicate by itself. Thus there is division of functions between the Land S particles. Infectivity can be initiated by L particles alone, but results in the production of nucleic acid only, not the entire virus. Lesions containing only nucleic acid are said to be of the 'summer type' or 'multiplying' (M) type. Lesions containing the entire virus are of 'winter type' or 'nonmultiplying' (NM) type.
Lesions produced by L particles are almost entirely of the winter type (NM). Those produced by inoclulation of S particles are of the summer type (M).Stable infections are produced by interaction of L and S particles. Heterologous mixtures of strains only distantly related serologically do not produce stable infections. Both short and long particles of PRN and GAM strains are built from one kind of protein subunit organized in helical symmetry. The molecular weight of the protein subunit is about 24,000. The protein subunits arc organized in a similar manner to that of TVM. The pitch of the helix is 2.5 nm, and there are 76 subunits in three turns. The diameter of both short and long particles is 25.6:1: 0.3 nm, with a hole diameter of 5.4 nm.
Electron microscope studies of a Dutch strain similar to PRN show that the short particles consist of 26 turns and therefore contain 660 protein subunits. The long particles have 72 turns, and therefore consist of 830 units. The MW of the RNA of the long particles is 2.3*106, corresponding to 7,100 nucleotides. If 1,830 protein subunits are assumed in a tong particle, then four nucleotides react with a protein subunit. This is in contrast with TMV where only three nucleotides react with a subunit. The RNA of the short particle of the PRN strain has MW of 0.7x 106 daltons, corresponding to 2,400 nucleotides. The base compositions of short PRN and long RNA of TRY CAM are significantly different. Semancik (1966) has, however, reported similar composition of the two RNAs in the California strain of TRV.

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