GENETIC ELEMENTS OF PLANT-VIRUSES AS TOOLS FOR GENETIC-ENGINEERING

Viruses have developed successful strategies for propagation at the ex pense of their host cells. Efficient gene expression, genome multiplic ation, and invasion of the host are enabled by virus-encoded genetic e lements, many of which are well characterized. Sequences derived from plant DNA and RNA viruses can be used to control expression of other g enes in vivo. The main groups of plant virus genetic elements useful i n genetic engineering are reviewed, including the signals for DNA-depe ndent and RNA-dependent RNA synthesis, sequences on the virus mRNAs th at enable translational control and sequences that control processing and intracellular sorting of virus proteins. Use of plant viruses as e xtrachromosomal expression vectors is also discussed, along with the i ssue of their stability.