GO:0003714

Interacting selectively and non-covalently with a repressing transcription factor and also with the basal transcription machinery in order to stop, prevent, or reduce the frequency, rate or extent of transcription. Cofactors generally do not bind DNA, but rather mediate protein-protein interactions between repressive transcription factors and the basal transcription machinery. [GOC:txnOH, PMID:10213677, PMID:16858867]