PARAHOMOLOGOUS GENE TARGETING IN DROSOPHILA CELLS - AN EFFICIENT, HOMOLOGY-DEPENDENT PATHWAY OF ILLEGITIMATE RECOMBINATION NEAR A TARGET SITE

Drosophila cells in culture can be transformed by introducing exogenou s DNA carrying a selectable marker. Here we report on the fate of plas mids that contain an extended fragment of Drosophila DNA in addition t o the selectable marker. A small minority of the resulting transforman ts appear to arise from homologous recombination at the chromosomal ta rget. However, the majority of the insertions are the products of ille gitimate events in the vicinity of the target DNA, and they often caus e mutations in the targeted region. The efficiency of this process, it s homology dependence, and the clustering of the products define a nov el transformation pathway that we call ''parahomologous targeting.''