CHARACTERIZATION OF THE BASAL INHIBITOR OF CLASS-II TRANSCRIPTION NC2FROM SACCHAROMYCES-CEREVISIAE

Human NC2 utilizes a unique mechanism of repression of transcription b y associating with TBP and inhibition of preinitiation complex formati on, Here we have cloned two genes from Saccharomyces cerevisiae and fu nctionally characterized them as yeast NC2. We show that yeast NC2 bin ds to TBP as a heterodimer and represses RNA polymerase II transcripti on during assembly of the preinitiation complex. Yeast NC2 is highly h omologous to its human counterpart within histone fold domains. C-Term inal regions previously discussed to be important for repression in ma n are in part not conserved. The human alpha but not the beta subunit efficiently heterodimerizes and represses transcription in combination with the corresponding yeast subunit, Yeast and human NC2 inhibit tra nscription in the presence of yeast and human TBP. However, repression is optimal within one species. The N-terminus of human TBP supports r epression of transcription by human but not by yeast NC2.