Genomic HDAC3 sequence that extends from 1173bp upstream of the transcription start site to 771bp downstream of the 3'UTR, and which has been mutated to carry a combination of substitutions that abrogates interaction with the Smr protein (mutations are K47E, L60T, R61K, E118A, G119A, Q121V, H125K, N128Q and H129A). Silent mutations have been introduced to render the construct resistant to RNAi-mediated knockdown by the P{TRiP.HMS00087} transgene.