Intermediates in the disassembly of tobacco mosaic virus at alkaline pH Infectivity, self-assembly, and translational activities

The origin of multiple polypeptides of molecular weight below 110 000 encoded by tobacco mosaic virus RNA in the messenger-dependent rabbit reticulocyte lysate

Multiple polypeptides encoded by tobacco mosaic virus (TMV) RNA in the messenger-dependent rabbit reticulocyte lysate are not attributable to contaminating 3'-coterminal RNA fragments, multiple leaky termination codons or endonuclease activity opening-up legitimate or spurious internal initiation sites. Quantitative analysis of polypeptides encoded over a range of added RNA concentrations from 0.09 microgram X ml-1 to 180 micrograms X ml-1 compared with those synthesized in response to size-fractionated RNAs from a crude virus preparation, or with RNA extracted from the alkali-stable fraction of TMV suggest that apart from four legitimate virus-coded products of apparent Mr approx. 165 000, 110 000, 30 000 and 17 500 all other polypeptides arise from the overlapping 5'-proximal cistrons either by (i) site-selective endonucleolytic cleavage, (ii) sense codon misreading, or (iii) specific regions of secondary structure on TMV RNA which impede ribosome translocation.

Efficient translation of the coat protein cistron of tobacco mosaic virus in a cell-free system from Escherichia coli

Translation of tobacco mosaic virus (TMV) RNA in a cell-free system derived from Escherichia coli (MRE 600) reveals several discrete polypeptides in the Mr range of 10,000-50,000. The major product is a polypeptide of Mr 17,500 which comigrates with authentic TMV coat protein on sodium dodecyl sulphate/polyacrylamide gel electrophoresis. Structural investigations by peptide-mapping techniques and differential radiolabelling confirm that the major product is TMV coat protein with an N-terminal methionine. The major polypeptide product can be assembled in vitro into virus-like ribonucleoprotein particles. The structural and evolutionary implications of this observation, and the values of TMV in elucidating eukaryotic mRNA interactions with the prokaryotic protein-synthesizing machinery, are discussed.