Effect of freezing and thawing on the structure of turnip yellow mosaic virus

The uncoating of turnip yellow mosaic virus in vitro induced by freezing and thawing has been investigated using a variety of biochemical techniques including the aminoacylation capacity of the viral RNA and the ability of the RNA to stimulate protein synthesis, as well as physico-chemical techniques such as sucrose gradient centrifugation and electron microscopy by negative staining. In particular a fluorescence test has been developed that can serve as a routine method to quantify the RNA liberated during the freeze-thaw process. Escape of the viral RNA is a highly cooperative phenomenon: it depends critically on the virus concentration during freezing and thawing. Increasing the ionic strength or including foreign proteins diminish the escape of the RNA. The RNA is not damaged by this treatment and its liberation occurs without disruption of the viral capsid.