cis-acting elements for in trans complementation of replication-defective mutant of tobacco mosaic virus

We have shown that virus-encoded replicase components of tobacco mosaic virus (TMV) (130K/180K proteins) could complement a replication-defective mutant (LDR28) for viral replication in trans [Ogawa et al. Virology 185, 580–584 (1991)]. Using this trans-complementation system, we investigated the dispensability of regions of the 130K/180K protein genes as cis-acting elements for viral replication. A series of replication-defective mutants (LDRs) which had various deletions in the 130K/1 80K coding region were constructed. These were co-inoculated with a replication-competent mutant (LDCS29) into tobacco protoplasts. Accumulation of LDR-genomic RNA, CP mRNA, and CP was much increased by the removal of the 3′ terminal one-third of the readthrough part of 180K protein gene (residues 4529–4937 of TMV-RNA) from LDR, suggesting that this region interferes with the viral replication in this trans-complementation system. In addition, accumulation of CP mRNA and CP was much decreased by the removal of the 5′ terrminal half of the 30K protein gene (residues 4938–5263 of TMV-RNA), suggesting the presence of an element to enhance the synthesis of CP mRNA in this region.