(A) EECs or EECs with Gdown1, EEC(G)s, were incubated with factors or extract and allowed to elongate for 6 min. in the presence of increasing amounts of TFIIS (0, 0.5, 1.5 or 5 pmole). (B) The effects of TFIIS (S) and TFIIF (F) were examined on the indicated elongation complexes. Elongations complexes were EECs or EEC(G)s. Abortive elongation complexes, AEC(G)s, are EEC(G)s in the presence of a HNE with FP. Productive elongation complexes are EEC(G)s incubated with HNE, extra P-TEFb and ATP for 5 minutes and then chased in the presence of FP. Elongation complexes were washed with 1.6 M salt (HSW) before the chase. Chases were for 6 min. and contained the indicated elongation complexes alone or were supplemented with TFIIS, or TFIIF. Details are present in the Experimental Procedures and in the text. The asterisk above lane 13 in A signifies that although no TFIIS was added, the extract present does contain TFIIS.