Tobacco mosaic virus nucleoprotein

The spectrophotometric evidence reviewed above for the binding of a proportion of the phenolic hydroxyl groups of the tyrosine residues of native proteins is supported by work on the action of tyrosinase on proteins. Sizer (1946) found that this enzyme oxidizes the tyrosine residues in native trypsin, pepsin, chymotrypsin, casein, peptone, insulin, and hemoglobin. Native ovalbumin, human and bovine serum albumin, tobacco mosaic virus (nucleoprotein), human y- and bovine /3-globulins, and bovine fibrinogen are not susceptible to tyrosinase, but become so after tryptic digestion. It was shown (Sizer, 1947) that for the proteins which are oxidized by tyrosinase in the native state, the observed reaction does indeed occur with the intact proteins and does not require preliminary degradation to tyrosine peptides or free tyrosine. The kinetics of the oxidation of tyrosine by tyrosinase have been studied spectropho-tometrically (Mason, 1948 etc.). 

II A radically different type of nucleoprotein is that provided by the smaller RNA viruses of the elongated spiral type like tobacco mosaic, or of the polyhedral type such as tomato bushy stunt, tipula virus or poliomyelitis virus. The only one of these adequately studied has been tobacco mosaic virus, Franklin [19, 20], and here it appears that the protein and not the nucleic acid determines the structure. There is only one RNA chain and this is wound helically so that one protein is in contact with three successive nucleotides. 

These are the facts which point to RNA being the template on which the synthesis of proteins takes place. Another confirmation has been brought by experiments showing that the isolated nucleic acid of tobacco mosaic virus can introduce the disease into a leaf cell as well as the whole nucleoprotein of the virus. 

Composition of Virus Particles. Many viruses have been prepared pure, some even in crystalline form. The simplest among them chemically are nucleoproteins they consist of protein and nucleic acid (usually DNA with some plant viruses, e.g. tobacco mosaic virus, it is RNA). Larger viruses are more variable, which means they can no longer be regarded as chemically definable nucleoproteins. 

Nucleoproteins Tobacco mosaic virus infected 95 5 RNA 0.725 0.728(2) 37B1,44L1,49S1, -0.4... 

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