A product comprising two or more artificial transcription repressors (ATRs), or polynucleotides encoding therefor, selected from groups (a), (b), (c) or (d): (a) an ATR comprising a DNA-binding domain operably linked to a KRAB domain or homologue thereof (b) an ATR comprising a DNA-binding domain operably linked to a DNMT3A, DNMT3B or DNMT1 domain or homologue thereof (c) an ATR comprising a DNA-binding domain operably linked to a DNMT3L domain or homologue thereof and (d) an ATR comprising a DNA-binding domain operably linked to a SETDB1 domain or homologue thereof, wherein at least two of the ATRs are selected from different groups (a), (b), (c) or (d).
