HORIZONTAL ESCAPE OF THE NOVEL TC1-LIKE LEPIDOPTERAN TRANSPOSON TCP3.2 INTO CYDIA-POMONELLA GRANULOVIRUS

We characterized an insertion mutant of the baculovirus Cydia pomonell a granulovirus (CpGV), which contained a transposable element of 3.2 k b, This transposon, termed TCp3.2, has unusually long inverted termina l repeats (ITRs) of 756 bp and encodes a defective gene for a putative transposase. Amino acid sequence comparison of the defective transpos ase gene revealed a distant relationship to a putative transposon in C aenorhabditis elegans which also shares some similarity of the ITRs, M aximum parsimony analysis of the predicted amino acid sequences of Tc 1- and mariner-like transposases available from the GenBank data base grouped TCp3.2 within the superfamily of Tc1-like transposons, DNA hyb ridization indicated that TCp3.2 originated from the genome of Cydia p omonella, which is the natural host of CpGV, and is present in less th an 10 copies in the C. pomonella genome. The transposon TCp3.2 most li kely was inserted into the viral genome during infection of host larva e. TCp3.2 and the recently characterized Tc1-like transposon TC14.7 (J ehle et al. 1995), which was also found in a CpGV mutant, represent a new family of transposons found in baculovirus genomes, The occasional horizontal escape of different types of host transposons into baculov irus genomes evokes the question about the possible role of baculoviru ses as an interspecies vector in the horizontal transmission of insect transposons.