Identification and sequence analysis of the integration site of transposon TCp3.2 in the genome of Cydia pomonella granulovirus

Recently, we described the isolation and characterisation of the novel lepidopteran transposon TCp3.2, which was found to be inserted into the genome of a spontaneous mutant of the baculovirus Cydia pomonella granulovirus (CpGV). Transposon TCp3.2, which is a member of the Tc1/mariner superfamily, is an apparently defective copy which became stably integrated into the viral genome (Jehle et al., 1997. J. Mol. Evol., in press). In this study, we located, cloned and sequenced a genomic region of 2.5 kb of CpGV which encompasses the insertion site of TCp3.2. The TCp3.2 was inserted at a TA dinucleotide as it is typical for many Tc1/mariner-like transposons. The TA insertion site was localised within a non-translated region downstream of the homologous gene of baculovirus late expression factor 2 (lef-2). Additionally, three other complete open reading frames (ORF35Ra, ORF35Rb, and ORF36L) with unknown functions were identified. Transposon insertion into intergenic regions of viral genomes may contribute to the genotypic variability of baculoviruses without any phenotypic effect.