THE MULTIPLICATION IN PLANTS OF ARABIS MOSAIC-VIRUS SATELLITE RNA REQUIRES THE ENCODED PROTEIN

Oligonucleotide-directed mutagenesis was used to create two mutations at each of three positions within the open reading frame (ORF) of a cD NA clone representing a satellite RNA from a lilac isolate of arabis m osaic nepovirus (ArMV). Three of the six mutants, in which stop codons were introduced at three different sites, did not direct synthesis of a translation product. The other three mutants, in which stop codons were not introduced, directed synthesis of a translation product (39K) although, in two of these, the mutation led to a single amino acid su bstitution. When Chenopodium quinoa plants were inoculated with in vit ro transcripts from each of the six mutants together with the genomic RNA molecules (RNA-1 and RNA-2) of ArMV, progeny RNA was detected only with two of the three mutants in which the nucleotide changes did not introduce a stop codon to the coding region. To look for complementat ion. two deletion mutants were made. In these, 113 or 117 nucleotides were removed from two consecutive regions within the ORF. Two insertio n mutants (in which the deleted sequences were replaced with a 130 nuc leotide sequence from RNA-2 of cherry leaf roll nepovirus) were also m ade. Transcripts from none of these mutants retained messenger activit y and none was detected either in C quinoa plants or in virions, even in the presence of wild-type satellite RNA.