Binding of multiple factors to the MMTV promoter in crude and fractionated nuclear extracts.

Hormone activation of MMTV transcription results in the establishment of a tightly bound transcription factor complex at the promoter (Cordingley et al., Cell 48, 261-270, 1987). We have characterized two fractionable binding activities which participate in this complex. One factor, previously identified as the mouse homologue of NF-1 (or CTF), protects sequences -82 to -56 from exonuclease III digestion in vitro. Sequences protected by a second factor (-42 to -4) span the TATA box of the promoter, suggesting that the binding activity in this fraction is equivalent to the HeLa cell transcription factor TFIID (Sawadogo and Roeder, Cell 43, 165-175, 1986). The downstream boundary of exonuclease protection by the putative TATA-binding factor is -4; DNase1 footprinting of this fraction, however, showed additional protection of discrete sites downstream of the cap site. The apparent concentration and promoter-specific binding activity of both factors is unaffected by hormone treatment of the cells.