Regulation of caulimovirus gene expression and the involvement of cis-acting elements on both viral transcripts.
In a further analysis of gene regulation of figwort mosaic virus (FMV), a caulimovirus, we studied transient gene expression with modified viral genomes in Nicotiana edwardsonii cell suspension protoplasts. The results demonstrated that the presence of the promoter for the full-length RNA interferes with expression from the separate downstream promoter for gene VI. In addition, expression of gene VI was inhibited by cis-acting sequences within gene VI itself. Both inhibitory effects could be partially relieved by coelectroporation with a plasmid that produces gene VI protein, demonstrating that expression of gene VI is transactivated by its own product. Subsequent expression studies with partially redundant FMV plasmids containing a reporter gene in frame with gene IV showed that efficient transactivation of CAT expression relies on a cis-acting element inside the downstream gene VI. Insertions of a transcriptional terminator upstream of the cis-acting element for premature termination of transcription showed that the cis-acting region is not a DNA element but is active only as a feature of the RNA transcript. We conclude that the cis-acting element, together with the transacting gene VI product, enhances expression of all major genes, including gene VI, from the polycistronic mRNA and the separate mRNA for gene VI.
Scholthof
H B
HB
Department of Plant Pathology, University of Kentucky, Lexington 40546-0091.
Wu
F C
FC
Gowda
S
S
Shepherd
R J
RJ
D004742:Enhancer Elements, Genetic; D015967:Gene Expression Regulation, Viral; D009029:Mosaic Viruses / Q000235:genetics*; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic; D015533:Transcriptional Activation