Use of Snake Venom Phosphodiesterase in Place of Pancreatic Ribonuclease for the Testing of Nucleic Acid Preparations from Tobacco Mosaic Virus

Abstract

DEPROTEINIZED plant virus preparations are customarily incubated with pancreatic ribonuclease in order to show that their infectivity is not due to residual virus particles. With tobacco mosaic virus nucleic acid, exceedingly small concentrations of the enzyme (10⁻⁸ mgm./ml.) are sufficient to abolish infectivity after incubation for 24 hr. at room temperature, whereas tobacco mosaic virus is not affected by a thousandfold higher concentration¹. However, under these conditions tobacco mosaic virus nucleic acid incubated without enzyme often loses most or all of its activity¹. Shorter times of incubation necessitate the use of higher ribonuclease concentrations, but at higher concentrations pancreatic ribonuclease, when mixed with plant viruses, inhibits infection^2–4. This effect occurs immediately after ribonuclease is mixed with the virus and does not increase upon incubation of the mixture². Consequently, as the ribonuclease concentration is increased and the incubation period shortened, the range within which tobacco mosaic virus nucleic acid is inactivated and tobacco mosaic virus is not affected becomes progressively narrower. If one considers that the effect on the virus of a given concentration of ribonuclease is furthermore a function of salt concentration and of concentration of tobacco mosaic virus², it becomes evident that the results of incubation studies with ribonuclease must be carefully evaluated before definite conclusions can be drawn.