Interaction of CAP sequence site binding factor and transcription factor IID preceding and following binding to the adenovirus 2 major late promoter

Since the mass of the cloned TFIIDs is considerably less than that of native hTFIID (27-38 kDa uersus 120-140 kDa), it is considered likely that native hTFIID exists as a mixed heterodimer.We have recently identified, purified, and characterized a novel transcription factor that binds to the CAP site region (+1 to +23) of the Ad2 MLP.This CAP site binding factor, designated CBF, is required for optimal transcriptional activity.We now show that when bound to the Ad2 MLP, yTFIID and CBF interact to generate the extended pattern of DNase I protection conferred by native hTFIID.In addition, bound yTFIID and CBF interact such that the stability of the complex exceeds that of each factor bound alone.We also demonstrate the existence in nuclear extracts of a hTFIID and CBF heterodimer by the electrophoretic mobility shift analysis.CBF, therefore, may represent the first identified member of a large family of gene-specific TFIIDassociated factors that are required for the regulated gene-specific expression of TFIID activity.Assembly of a functional transcription complex at the adenovirus 2 major late promoter (Ad2 MLP)' is thought to