The human general co-factors.

The human general co-factors were discovered during biochemical fractionation of mammalian nuclear extracts in functional in vitro assays. They appear to act in concert with other co-activators that bind tightly to the TATA-binding protein and RNA polymerase II. Several co-factors have been shown to interact with general transcription factors, leading either to activation or repression of transcription. At least one subgroup of co-factors that enhance the effects of activators on transcription are DNA-binding proteins located in the chromatin. In fact, one co-factor, the repressor NC2, is structurally related to histones. The understanding of the molecular interplay of such components of the initiation complex in the chromatin-including general co-factors, other co-factors, general factors and activators-will be a major challenge in the future.