PREFERENTIAL REPLICATION OF DEFECTIVE TURNIP YELLOW MOSAIC-VIRUS RNASTHAT EXPRESS THE 150-KDA PROTEIN IN CIS

The turnip yellow mosaic virus genome encodes two proteins (the 150-kD a and 70-kDa proteins) that are proteolytically released from a single precursor and which are essential for RNA replication. Genomes with m utations in either of these coding regions were defective for independ ent replication in turnip protoplasts. The replication in trans of gen omes with mutations in each region was studied by coinoculation with e ither a helper genome that carries a deletion in the coat protein gene , or with a second defective RNA that carries a mutation in the region encoding the other essential protein. Inefficient trans-replication o f the defective RNAs was observed in most cases. In contrast, a defect ive RNA with a large deletion in the 70-kDa protein coding region coul d be replicated efficiently in trans, demonstrating that the cis-prefe rence of replication can be overcome in some cases. Defective RNAs enc oding wild type 150-kDa protein and defective 70-kDa protein were more efficiently replicated in trans than those encoding defective 150-kDa protein and wild type 70-kDa protein. The results suggest a model in which the 150-kDa and 70-kDa proteins form a relatively stable complex in cis on the viral RNA template.