POLYDNAVIRUS DNA OF THE BRACONID WASP CHELONUS-INANITUS IS INTEGRATEDIN THE WASPS GENOME AND EXCISED ONLY IN LATER PUPAL AND ADULT STAGES OF THE FEMALE

Many endoparasitic wasps inject, along with the egg, polydnavirus into their insect hosts, the virus being a prerequisite for successful par asitoid development. The genome of polydnaviruses consists of multiple circular dsDNA molecules of variable size. We show for a 12 kbp segme nt of the braconid Chelonus inanitus (CiV12) that it is integrated int o the wasp genome. This is the first direct demonstration of integrati on for a bracovirus. PCR data indicated that the integrated form of Ci V12 was present in all male and female stages investigated while the e xcised circular virus DNA only appeared in females after a specific st age in pupal-adult development. The data also indicated that after exc ision of virus DNA the genomic DNA was rejoined. This has not yet been reported for any polydnavirus. Sequence analyses in the junction regi ons revealed the presence of an imperfect consensus sequence of 15 nuc leotides in CiV12, in each terminus of the integrated virus DNA and in the rejoined genomic DNA. Within these repeats two sequence types (AT A, TAC) were observed in the various virus clones and in the clones en compassing the rejoined genomic DNA; they corresponded to the sequence type in the right and left junction, respectively. To explain this, w e propose a model of virus DNA replication in which the genomic DNA is folded to juxtapose the direct repeat of the left with that of the ri ght junction; recombination at specific sites would then yield the two types of virus and rejoined genomic DNA.