Transgenic construct used to study a Polycomb Group response element (PRE) from the en locus. Generated using the pP{CaSpeR} vector; a mutated 'PRE2' en fragment (extending from -576 to -395bp relative to the en transcription start site), which has been altered to contain mutations in pho protein-binding site 'Pho2', has been inserted upstream of the w+mC minigene.