Fig. 3.

TFIIS stimulates formation of active PICs. PICs were assembled by incubating nuclear extracts from either a wild-type strain or a strain lacking DST1 with the indicated promoters in the presence or absence of Gal4-AH (1.5 pmol) or Gal4-VP16 (1 pmol) for 60 min. rTFIIS (3 pmol) was included where indicated. Transcription was initiated by the addition of NTPs, and reactions were stopped after 2 min. Brackets indicate correctly initiated transcripts that were detected by primer extension. The fold stimulation was calculated by comparing the transcription signal in reactions supplemented with rTFIIS to those lacking TFIIS.