Extrachromosomal replication of copia-based vectors in cultured Drosophila cells

The functional analysis of cloned Drosophila genes in vivo has so far not been possible because of the lack of an appropriate cultured cell transformation system. We have developed a transformation method which uses the Escherichia coli gene coding for xanthine guanine phosphoribosyl transferase (gpt)1, inserted into a cloned copia2transposable element, and a medium selective for transformed cells expressing the gpt gene. We show that the resulting plasmids (pCVgpt) propagate extrachromosomally in transformed cells, apparently without integrating into the genome. This suggests that the extrachromosomal copia circles found in Drosophila tissue-culture cells may also replicate semi-conservatively.