Probable histone demethylase that specifically demethylates 'Lys-4' of histone H3, a specific tag for epigenetic transcriptional activation, thereby acting as a corepressor. Required for heterochromatic gene silencing. Acts by oxidizing the substrate by FAD to generate the corresponding imine that is subsequently hydrolyzed. Demethylates both mono- and tri-methylated 'Lys-4' of histone H3. May also demethylate 'Lys-9' of histone H3, Plays a role in the repression of neuronal genes. Component of a complex that contains at least HDAC1/Rpd3, CoRest and Su(var)3-3/Hdm. In early cleavage, protein displays a uniform nuclear distribution. At metaphase, protein is detected at the chromosome periphery, and between the chromosomes during anaphase. A rather uniform interphase chromatin association is detected until syncytial blastoderm. When cellular blastoderm is formed (cycle 14), protein is preferably associated with pericentric heterochromatin situated at the apical pole of blastoderm nuclei. Later in development, protein is only found over euchromatin. In the germline precursor pole cells, protein remains uniformly distributed within the nucleus. Belongs to the flavin monoamine oxidase family.