THE RNA of tobacco mosaic virus (TMV) can be translated in various cell-free systems1–3 and in amphibian oocytes4, to yield two large polypeptides of molecular weights (MW) approximately 110,000 (110K) and 160,000 (160K). Products of the same sizes are found in infected plants2,5 and protoplasts6 and they are probably components of the viral replicase7,8. I show here that synthesis of these two proteins is initiated at the same site; the larger product is generated by partial readthrough of an amber (UAG) termination codon, and in the presence of yeast amber suppressor tRNA, the in vitro synthesis of the 160K protein is increased whereas the yield of the 110K protein is diminished.

Leaky UAG termination codon in tobacco mosaic virus RNA.

— Myelin was purified from rats which had been injected intracerebrally with radioactive fucose in order to label specifically the glycoproteins. Myelin contained a small amount of fucose-labelled glycoproteins in comparison to that in other subcellular fractions, but polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate revealed a unique pattern of radioactive glycoproteins dominated by a major peak. The same glycoprotein was not prominent in the other subcellular fractions which were examined. This major glycoprotein in the myelin fraction was also labelled after injection with [3H]glucosamine or N-[3H]acetylmannosamine. It was the most intensely staining myelin protein when gels were treated with periodic acid-Schiff reagents, an indication that, in terms of protein-bound carbohydrate, it is the major glycoprotein in the myelin fraction. The glycoprotein was present in myelin purified from rats ranging in age from 14 days to 14 months. Extensive recycling of the myelin through the purification procedures did not significantly reduce the amount of glycoprotein in the myelin. Double label experiments with [3H]fucose and [14C]fucose were used to compare glycoproteins in myelin purified from white and grey matter, respectively, and from mixed homogenates of myelinated and unmyelinated brain. The results obtained from these experiments suggested that the glycoprotein is closely associated with myelin and that it is not in an unrelated contaminating structure. Possible locations of the glycoprotein are discussed. They include the myelin membrane itself, the oligodendroglial plasma membrane, and the axolemma of myelinated axons.

Evidence for the close association of a glycoprotein with myelin in rat brain.

In vitro and in vivo translation of the ribonucleic acids of a cowpea strain of tobacco mosaic virus

Light-stimulated incorporation of N-ethylmaleimide into coupling factor 1 in spinach chloroplasts.

Role of the gamma subunit of chloroplast coupling factor 1 in the light-dependent activation of photophosphorylation and ATPase activity by dithiothreitol.

A gel electrophoretic analysis of proteins from plants infected with tobacco mosaic and potato spindle tuber viruses.

An improvement in a procedure for counting tritium and carbon-14 in polyacrylamide gels.

Proteins in tobacco mosaic virus-infected tobacco plants.

A temperature-sensitive mutant of TMV with unstable coat protein.

Insoluble coat protein mutants of TMV: their origin, and characterization of the defective coat proteins.

V. Hariharasubramanian

Papers

A gel electrophoretic analysis of proteins from plants infected with tobacco mosaic and potato spindle tuber viruses.

An improvement in a procedure for counting tritium and carbon-14 in polyacrylamide gels.

Proteins in tobacco mosaic virus-infected tobacco plants.

A temperature-sensitive mutant of TMV with unstable coat protein.

Insoluble coat protein mutants of TMV: their origin, and characterization of the defective coat proteins.