EUKARYOTIC ACTIVATORS FUNCTION DURING MULTIPLE STEPS OF PREINITIATIONCOMPLEX ASSEMBLY

Eukaryotic activator proteins (activators) stimulate transcription by increasing assembly of the preinitiation complex. We have developed me thods to quantify the stable assembly of general transcription factors into transcriptional complexes in response to activators. We show tha t activators function during at least two stages of preinitiation comp lex assembly: first, to recruit the general transcription factor TFIIB , and then at a second step, after TFIIB entry. It is at this second s tep that the TATA-box binding protein associated factors act. This ste p also seems to be critical for activators to stimulate transcription synergistically.