Drosophila Chorion Gene Amplification: A Model System for the Study of Chromosome Replication

Two chromosomal domains of 80-100 kilobases containing Drosophila chorion genes undergo tissue-specific amplification in ovarian follicle cells during oogenesis. We have investigated the ability of small segments of DNA from within these regions to induce amplification after insertion into new chromosomal sites by P element-mediated transformation. Certain transduced chorion DNA sequences initiated a pattern of tissue-specific differential replication that was identical to normal chorion amplification. Both the transformed chorion DNA as well as flanking rosy DNA sequences underwent amplification. Our results suggest that differential chorion DNA replication is mediated by specific origin-containing sequences located near the centre of the amplified domains. The possible role of such sequences in normal programmes of replication is discussed.