THE SECONDARY STRUCTURE OF THE 5'-NONCODING REGION OF BEET NECROTIC YELLOW VEIN VIRUS RNA-3 - EVIDENCE FOR A ROLE IN VIRAL-RNA REPLICATION

Secondary structure-sensitive chemical and enzymatic probes have been used to produce a model for the folding of the first 312 residues of the long 5'-noncoding region of beet necrotic yellow vein virus RNA 3. The structure consists of two major domains, one of which includes long distance base-pairing interactions between two short sequence elements (Box I and Box II) situated between positions 237 and 292 and complementary elements (Box I' and II') near the 5'-terminus. Previous studies have shown that base pairing between these sequence elements (in either the plus-strand or minus-strand RNA) is important for RNA 3 accumulation during infection. RNA 3 transcripts were produced containing mutations which preferentially disrupted Box II-II' base pairing in either the plus- or minus-strand. In infection experiments, transcripts with mutations which disrupted the Box II-II' interaction in the plus-strand structure replicated less efficiently than mutants in which the Box II-II' interaction was disrupted in the minus-strand. These findings indicate that the complex 5'-proximal plus-strand structure to which the Box II-II' interaction contributes comprises at least part of the promoter for plus-strand RNA synthesis.