A P-ELEMENT CONTAINING SUPPRESSOR OF HAIRY-WING BINDING REGIONS HAS NOVEL PROPERTIES FOR MUTAGENESIS IN DROSOPHILA-MELANOGASTER

P elements are widely used as insertional mutagens to tag genes, facil itating molecular cloning and analyses. We modified a P element so tha t it carried two copies of the suppressor of Hairy-wing [su(Hw)] bindi ng regions isolated from the gypsy transposable element. This transpos on was mobilized, and the genetic consequences of its insertion were a nalyzed. Gene expression can be altered by the su(Hw) protein as a res ult of blocking the interaction between enhancer/silencer elements and their promoter. These effects can occur over long distances and are g eneral. Therefore, a composite transposon (SUPor-P for suppressor-P el ement) combines the mutagenic efficacy of the gypsy element with the c ontrollable transposition of P elements. We show that, compared to sta ndard P elements, this composite transposon causes an expanded reperto ire of mutations and produces alleles that are suppressed by su(Hw) mu tations. The large number of heterochromatic insertions obtained is un usual compared to other insertional mutagenesis procedures, indicating that the SUPor-P transposon may be useful for studying the structural and functional properties of heterochromatin.