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Concentration of Wound Tumor Virus Determined from Absorbance of the RNA of Virus Collected on Filters. Ikuo Kimura, Provisional Department of Genetics and Development, University of Illinois, Urbana 61801, Present address: Institute for Plant Virus Research, 959 Aoba, Chiba 280, Japan; L. M. Black, Provisional Department of Genetics and Development, University of Illinois, Urbana 61801. Phytopathology 66:371-378. Accepted for publication 8 September 1975. DOI: 10.1094/Phyto-66-371.

Counts of purified wound tumor virus (WTV) particles in an electron microscope were correlated with the ultraviolet absorbance of their extracted RNA. The regression equation for the correlation is C = (0.935 ± 0.0146) A + (0.012 ± 0.0049) where C = number of virions (× 1012) per ml and A = absorbance at a wavelength of 258 nm. The purified virus, which has a diameter of ~70 nm, was collected from solution onto Millipore filters with an average pore diameter of 50 nm. The RNA was extracted by placing the filter with its virus deposit in 2 ml of 1 N HCl and maintaining the preparation at 24 to 30 C for 20 to 24 hours. Accurate WTV-RNA readings could be made on virus from 2-g samples of tumors when such filters were used to collect the virus, whereas with samples seven times larger, less than half the WTV-RNA was recovered when virus was collected by centrifugation into a pellet.