MECHANISM OF PROMOTER SELECTION BY RNA POLYMERASE-II - MAMMALIAN TRANSCRIPTION FACTORS ALPHA AND BETA-GAMMA PROMOTE ENTRY OF POLYMERASE INTO THE PREINITIATION COMPLEX

Productive binding of RNA polymerase 11 at the core region of TATA box-containing promoters is controlled by the action of the TATA factor and four additional transcription factors, designated alpha, beta-gamma, delta, and epsilon, which have each been purified to near homogeneity from rat liver. This process is accomplished in three distinguishable stages. In the first stage (initial complex formation), the core promoter is packaged with the TATA factor into a binary complex that serves as the recognition site for RNA polymerase 11. Here we show that, in the second stage (site selection), transcription factors alpha and beta-gamma-act in combination to promote selective binding of RNA polymerase II to the initial complex. Several lines of evidence argue that alpha and beta-gamma-function at this stage by a mechanism related to that utilized by bacterial sigma-factors. In the third stage, transcription factors delta and epsilon promote assembly of the functional preinitiation complex. Our evidence supports the model that delta and epsilon enter the preinitiation complex and direct formation of stable protein-DNA contacts that anchor the transcription apparatus to the core promoter at sequences near the cap site.