After the co-infection of larvae of the lepidopteran Cryptophlebia leu
cotreta with the two baculoviruses C. leucotreta granulosis virus and
Cydia pomonella granulosis virus (CIGV and CpGV, respectively), three
CpGV mutants and one CIGV mutant carrying insertions of 0.9 to 4.7 kb
have been isolated. By cloning, sequencing, and hybridization analysis
, one of these insertions was identified as a transposon-like element
derived from the C. leucotreta genome. This element, called TCl4.7, wa
s found in the genome of CpGV which naturally replicates in C. pomonel
la. Sequence analysis suggested that TCl4.7 is 4726 bp in size, flanke
d by imperfect inverted terminal repeats of 29 bp, and integrated into
the target dinucleotide TA. TCl4.7 encompasses an open reading frame
sharing homologies to transposase genes of the Tc1-related transposabl
e elements found in Caenorhabditis and in Drosophila species. The open
reading frame might represent a pseudogene since it is missing an ATG
start codon. The integration site of TCl4.7 is located in a non-prote
in-coding region of the CpGV genome at m.u. 9.5, In bioassays the TCl4
.7-carrying virus and all the other mutants except for one showed LC(5
0) values similar to those of CpGV and CIGV. This is the first report
of the horizontal escape of a transposable element during the in vivo
infection of lepidopteran larvae by granulosis viruses. (C) 1995 Acade
mic Press, Inc.