A protein or a member of a complex that interacts specifically and non-covalently with a DNA-bound DNA-binding transcription factor to either activate or repress the transcription of specific genes. Coregulators often act by altering chromatin structure and modifications. For example, one class of transcription coregulators modifies chromatin structure through covalent modification of histones. A second ATP-dependent class modifies the conformation of chromatin. A third class modulates interactions of DNA-binding transcription factor with other transcription coregulators. [ http://www.ncbi.nlm.nih.gov/pubmed/24203923 http://www.ncbi.nlm.nih.gov/pubmed/10213677 http://en.wikipedia.org/wiki/Transcription_coregulator http://www.ncbi.nlm.nih.gov/pubmed/16858867 http://www.ncbi.nlm.nih.gov/pubmed/25957681 ]