SUMMARY: Studies of the products obtained when tobacco Mosaic virus (TMV) is disrupted with alkali or phenol suggest that immunological specificity is primarily an attribute of the protein and infectivity of the nucleic acid. Although exposing the much of the nucleoprotein sedimented when preparations are ultracentrifuged at pH 6 is not infective. The unsedimented protein fragments are inhibitors of infection; from such unsedimentable material, which at 5 g./l. produced no lesion when inoculated to , some infective nucleoprotein could sometimes be separated by precipitation with ammonium sulphate, followed by ultracentrifugation. The infectivity of fragmented TMV is ephemeral, but it is stabilized when the fragments are reunited. Nucleic acid preparations made by phenol are quickly inactivated by ribonucleases from pancreas or leaves; pancreatic ribonuclease also inactivates alkali-made fragments, but the infectivity of these is stabilized by leaf ribonuclease. Phenol-made preparations are much less infective per unit of phosphorus than intact TMV, but measurements of the relative infectivities of two kinds of inocula are complicated because the two respond differently to dilution and they are not equally able to infect leaves in differently to dilution and Although urea does not inactivate phenol-made preparations, physilogical states, exposing TMV to urea has little or no infectivity. The possibility that infective TMV can be reassembled from previously non-infective components cannot be excluded, but all the results that could be interpreted as suggesting this are also interpretable in other ways, either by the removal of inhibitions of infection or by the stabilization of infective fragments that otherwise would have become inactive before testing.


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