When purified preparations of the isolate of tobacco rattle virus were stored the protein in the virus particles underwent limited proteolysis. Using polyacrylamide gel electrophoresis, a change was observed in the mol. wt. of the virus polypeptide from 28 500 to 23 500, and in some instances a possible intermediate of 26 000 mol. wt. was detected. Polypeptides of mol. wt. 13 500, 11 500 and 9000 were also detected after prolonged storage. Virus protein was not degraded when virus preparations containing sodium azide or antibiotics were stored, but it was degraded in the presence of azide when incubated with the supernatant fluid obtained by centrifuging preparations of virus which had been stored for several months without bacteriostatic additive. The proteolysis was probably caused by microbial exoenzyme(s). The conversion of polypeptide from mol. wt. 28 500 to 23 500 did not affect sedimentation coefficient, behaviour when centrifuged to equilibrium in caesium chloride, appearance in the electron microscope, serological reactivity, infectivity, heat stability or resistance of infectivity to pancreatic ribonuclease.

Purified virus was not affected by treatment with trypsin or chymotrypsin whereas the virus polypeptide was degraded by pronase and by papain. Papain had effects similar but not identical to those of storage. These enzyme treatments did not greatly affect infectivity or alter the appearance of virus particles in the electron microscope.

Isolate was affected by storage and by papain treatment in the same way as isolate , but more slowly.


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