Densovirinae as gene transfer vehicles.

Densoviruses present an attractive opportunity to develop expression vectors for insects. They exhibit several features that are beneficial for such vectors. The genomes of densoviruses are among the smallest of animal DNA viruses, and, therefore are easier to use for cloning and transfection procedures. The fact that cloned densovirus genomes are infectious greatly simplifies their applications. It seems that both densovirus promoters have high constitutive activity and they can be further transactivated with NS. The major nonstructural protein, NS1, can retain its functions even if fused to a foreign protein. If the recombinant genome carrying a gene of interest is supplied with the missing virus functions, it can be packaged into transducing particles. The packaging capacity of the densovirus particles can accommodate a foreign gene encoding a polypeptide of up to 150 kDa. Finally, the functions missing from the recombinant densovirus genome that are necessary for the production of transducing particles can be supplied in several different ways: they can be expressed from a helper plasmid, in cells transformed with the virus genes, or from an RNA virus. The last two methods produce transducing particles which are free of wild type virus. Densovirus transducing particles can be used for the delivery and expression of a gene of interest in insect cell culture or living insects. Transducing particles expressing reporter genes can be valuable tools in the study of viral pathogenesis and perhaps in the genetic manipulation of insects.