Characterization of the Oat-Infecting Strain of Maize Dwarf Mosaic Virus

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Abstract
Virions of an oat-infecting strain of maize dwarf mosaic virus (MDMV-O) were purified using 0.01 M Tris-citrate, pH 7.0, by differential centrifugation, rate-zonal centrifugation in sucrose gradients, and isopycnic banding in CsCl gradients. Satisfactory virion resuspension after high-speed centrifugation also was obtained with 0.01 M potassium phosphate, pH 7.4 containing 1-3 M urea. Purified virions measured 650 to 808 .times. 14 nm and had an s20,w of 168 S and a buoyant density of 1.297 g/ml in CsCl. Viral nucleic acid was digested by RNase but not DNase, and virions contained 6.6% RNA by weight as determined by ultraviolet absorbance. Three virions capsid-protein subunits were detected by sodium dodecyl sulfate-polyacylamide of gel electrophoresis (SDS-PAGE). The molecular masses (Mr) of the three protein subunits were estimated to be 35.1, 33.0 and 30.5 kDa. In contrast, single capside-protein subunits were observed for virions of MDMV strains A, D, E, and F in SDS-PAGE, whereas three were observed for MDMV-B virions with Mr similar to those for the virion capsid-protein subunits of MDMV-O. Serologically, MDMV-O was distantly related to strains A, B, D, and F of MDMV as determined by enzyme-linked immunosorbent, immunodotblot, and microprecipitin assays, and to MDMV strain E and sugarcane mosaic virus strain A, but not H, as determined by the microprecipitin assay.