Cucumber mosaic virus-associated RNA 5: III. Little nucleotide sequence homology between CARNA 5 and helper RNA

Abstract

Ribonuclease-resistant nucleic acid structures were isolated from plants infected with the S strain of cucumber mosaic virus (CMV). The behavior of these nucleic acids in relation to the corresponding single-stranded (ss) RNAs in rate zonal centrifugation experiments and/or in polyacrylamide gel electrophoresis suggested that they are the double-stranded (ds) RNAs of CMV and CMV-associated RNA 5 (CARNA 5). The yields of ds RNAs isolated from different host plants infected with CMV varied significantly. In host plant-inoculum combinations producing large amounts of CARNA 5, the dsRNAs consisted for 90% or more of dsCARNA 5, while yields of dsRNAs were two to five times higher than in the absence of dsCARNA 5. Separation of dsCARNA 5 from the viral dsRNAs was accomplished by rate zonal centrifugation on sucrose gradients, and resulted in a gel-electrophoretically pure product. This material hybridized with 3H-labeled CARNA 5. In competition hybridization experiments only 9% of the radioactivity of [ 3H]CARNA 5 would not have hybridized at infinitely high concentration of CMV RNA 1 + 2 + 3, and none with CMV RNA 4. Thus, CARNA 5 has no nucleotide sequence homology with CMV RNA 4, and, at most only 0.1 of its nucleotide sequence occurs in the genomic RNAs of CMV.