Transgenic construct used in a pairing-sensitive repression (PSR) assay. Generated by inserting a 4.9 kb EcoRI-PstI fragment from upstream of ph-p (nucleotides 74,925 to 70,027 of AE003423) into pCaSpeR4 (which contains the w+mC minigene). The orientation of the fragment relative to the w ORF is the reverse of its normal orientation relative to the ph-p transcription unit.