Preferential extrachromosomal localization of exogenous DNA in transgenic silkworm Bombyx mori L.

Transgenic silkworms (Bombyx mori L.) were obtained by microinjection of plasmid pPrC-LTR1.5, which carris 1.5 DNA copies of Rous sarcoma virus (RSV) long terminal repeats (LTRs) inserted in the vector pBR322. The transgene was transmitted over the three generations obtained up to now. Most of the exogenous DNA failed to integrate into the genome and persisted as an extrachromosomal element that is subject to rearrangements. Plasmids carrying only part of the input DNA together with fragments of silkworm DNA were rescued from the transgenic animals. One of the rescued plasmids contained a sequence which belongs to a family of evolutionarily conserved repeated sequences.