Extrachromosomal transposition of the transposable element Minos occurs inembryos of the silkworm Bombyx mori

To assess the ability of the transposable element Minos to act as a vector for genetic manipulation of the silkworm Bombyx mori, an extrachromosomal t ransposition assay based on three plasmids was performed. The three plasmid s - helper, donor and target - were co-injected into preblastoderm embryos. Low molecular weight DNA was extracted from the embryos at the stage of bl astokinesis and used to transform Escherichia coli. High frequency of trans position was observed in the presence of a helper plasmid possessing an int ronless Minos transposase gene, whereas transposition did not occur in the presence of a helper plasmid with the intron-bearing transposase gene. Sequ ence analysis of the insertion sites showed that Minos always inserts into a TA dinucleotide. Although the insertions are distributed throughout the t arget gene, there was a preference for certain insertion sites. However, no consensus could be identified in the sequence flanking the target site. Th e results strongly suggest that the transposable element Minos has the pote ntial to be used as a vector in the silkworm and probably in other lepidopt eran insects.