Near-zero linking difference upon transcription factor IID binding to promoter DNA

Binding of yeast transcription factor IID (TFIID) to the adenoviral major late promoter in circular DNA molecules caused a linking number change of less than 0.1. TFIID on its own therefore fails to unwind DNA appreciably, or else it causes both unwinding and compensatory writhing. Highly purified, recombinant yeast TFIID relaxed supercoiled DNA, because of a contaminant of bacterial topoisomerase I. Relaxing activity of topoisomerase I was enhanced by the adenoviral major late promoter, suggesting an instability of the TATA sequence or a destabilizing effect on flanking DNA.