Studies on the rate and site-specificity of P element transposition

A single genetically marked P element can be efficiently mobilized to insertionally mutagenize the Drosophila genome. We have investigated how the structure of the starting element and its location along the X chromosome influenced the rate and location of mutations recovered. The structure of two P[rosy⁺] elements strongly affected mobilization by the autonomous 'Jumpstarter-1' element. Their average transposition rates differed more than 12-fold, while their initial chromosomal location had a smaller effect. The lethal and sterile mutations induced by mobilizing a P[rosy⁺] element from position 1F were compared with those identified previously using a P[neo(R)] element at position 9C. With one possible exception, insertion hotspots for one element were frequently also targets of the other transposon. These experiments suggested that the genomic location of a P element does not usually influence its target sites on nonhomologous chromosomes. During the course of these experiments, Y-linked insertions expressing rosy⁺ were recovered, suggesting that marked P elements can sometimes insert and function at heterochromatic sites.