TARGETED TRANSPOSITION AT THE VESTIGIAL LOCUS OF DROSOPHILA-MELANOGASTER

Targeted transposition is the replacement of one P element with anothe r. We are exploiting this unique property of P elements to study the c omplex regulatory domain of the Dopa decarboxylase (Ddc) gene in Droso phila melanogaster. P element constructs targeted to the same site in the genome will be subjected to the same position effect. This allows the subtle effects typical of most mutations in the Ddc regulatory reg ion to be measured in the absence of the variable influences of positi on effects which are associated with the current method of germline tr ansformation. We have investigated some of the parameters affecting ta rgeted transposition of a Ddc transposon, P[Ddc], into a P element all ele at the vestigial locus. These events were detected by an increased mutant vg phenotype. The location of the donor transposon in cis or i n trans to the target had little effect on the frequency of targeting. Likewise, the mobility of different donor elements, as measured by th eir rate of transposition to a different chromosome, varied nearly 20- fold, while the rate of targeted transposition was very similar betwee n them. All targeted alleles were precise replacements of the target P element by P[Dcd], but in several cases the donor was inserted in the opposite orientation. The targeted alleles could be described as the result of a replicative, conversion-like event.