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Gene VI of Figwort Mosaic Virus (Caulimovirus Group) Functions in Posttranscriptional Expression of Genes on the Full-Length RNA Transcript
Siddarame Gowda, Fang C. Wu, Herman B. Scholthof and Robert J. Shepherd
Proceedings of the National Academy of Sciences of the United States of America
Vol. 86, No. 23 (Dec. 1, 1989), pp. 9203-9207
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/35048
Page Count: 5
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Experimental evidence for a molecular function for gene VI of the caulimoviruses is presented. Based on experiments with the figwort mosaic virus (FMV), it appears that gene VI has a role in the posttranscriptional expression of the closely packed genes (VII and I-V), which appear on the larger, full-length RNA transcript of this virus. Gene VI with its flanking 5′/3′ expression signals included as a separate plasmid during electroporation of DNA into protoplasts of Nicotiana edwardsonii shows an unusual type of transactivation of a chloramphenicol acetyltransferase (CAT) gene fused at its 5′ end to a small open reading frame (gene VII) of the long 5′ leader of the full-length RNA transcript of the FMV genome. The level of activity of the CAT gene is increased up to 20-fold over the activity of control plasmids when gene VI is included in the electroporation mixture. Mutagenesis of the coding portions of gene VI of pGS1 RVI, a transactivating plasmid used in the electroporation experiments, demonstrated that it was probably the polypeptide product of gene VI that was responsible for the transactivating effect. Experiments with various portions of the 5′ leader of the large, full-length RNA of FMV showed that the coding region of gene VII is necessary for the transactivation event. Clones of cauliflower mosaic virus (CaMV) or FMV with intact gene VI were found to reciprocally transactivate gene VII-CAT fusions (FMV) or gene I-CAT fusions (CaMV) located downstream of the 5′ leader sequences of either viral genome.
Proceedings of the National Academy of Sciences of the United States of America © 1989 National Academy of Sciences