Coincidence of P-insertion sites and breakpoints of deletions induced by activating P elements in Drosophila.

We isolated a set of seven deletions in the 67B region by activating a nearby P-element insertion. The structures of the deletions were characterized by cloning and sequencing. The results showed that the P-induced deletions occurred nonrandomly in the genomic sites. One breakpoint of the deletions was located precisely at the end of the starting element, i.e., at the end of the inverted terminal repeats. The other breakpoint was nearby the retained starting element and coincided with preferential P-element insertion sites that harbor transcription initiation activities. It is known that P elements induce male recombination near the starting elements, giving rise to deletions with one breakpoint precisely located at an inverted terminal repeat of the retained starting element. Database analyses further revealed that deletions generated in P-induced male recombination also contained the other breakpoint in genomic regions that coincided with preferential P-insertion sites. The results suggest that nonrandom distribution of the deletion breakpoints is characteristic of the mechanism by which P elements induce deletions near the starting elements.