CONTROL OF GENE-EXPRESSION IN PLANT-CELLS USING A 434 VP16 CHIMERIC PROTEIN/

The herpes simplex virus type 1 VP16 polypeptide is a potent trans-act ivator of viral gene expression. We have tested the ability of the VP1 6 activation domain to activate gene expression in plant cells. A plas mid encoding a translational fusion between the full-length 434 repres sor and the C-terminal 80 amino acids of VP16, was constructed. When e xpressed in Escherichia coli, the chimeric protein binds efficiently t o 434-binding motifs (operators). For expression in plant cells, the c himeric activator gene was placed between the cauliflower mosaic virus (CaMV) 35S promoter and nos terminator sequences in a pUC-based plasm id. The 434 operators were placed upstream of a minimal CaMV 35S promo ter linked to the E. coli gus reporter gene. This reporter-expression cassette was then incorporated into the same plasmid as the 434 cI/VP1 6 activator-expression cassette. Two control plasmids were also constr ucted, one encoding the 434 protein with no activator domain and the s econd a chimeric activator with no DNA-binding domain. The chimeric ac tivator was tested for its ability to activate gene expression in a to bacco protoplast transient assay system. Results are presented to show that we can obtain in plant cells significant activation of gene expr ession that is dependent on both DNA-binding and the presence of the a ctivator domain.