Isolation and properties of double-stranded viral RNA from virus-infected plants

Abstract

Nucleic acid preparations made from tobacco leaves infected with tobacco mosaic virus and Chinese cabbage leaves infected with turnip yellow mosaic virus contain a ribonuclease-resistant RNA fraction which can be isolated by sucrose density-gradient sedimentation or, more effectively, on columns of methylated bovine serum albumin on kieselguhr. The following facts indicate that for each virus the RNA is a double-stranded base-paired replicative form of the viral RNA; (1) it is present only in infected leaf; (2) its resistance to ribonuclease is lost on heating in low salt; (3) the material bands in Cs 2 SO 4 at a density > 1·60 g/ml.; (4) alkaline digestion gives the 3′-ribomononucleotides; (5) when infected leaf is labelled with 32 P for several days, the base ratios found are close to those expected for a double-stranded structure containing a viral RNA strand base-paired to a complementary RNA strand. The base ratios found after labelling for short times suggest that the viral RNA is replicated by an asymmetric semi-conservative process.