Transcriptional coregulator which can act as both a transcriptional corepressor and coactivator. Regulates p53-dependent and -independent DNA repair processes following genotoxic stress. Plays an important role in tumorigenesis, tumor invasion . Plays a role in the regulation of the circadian clock . May be involved in the regulation of gene expression by covalent modification of histone proteins. Isoform Long is a corepressor of estrogen receptor (ER).