Bm. Shykind et al., TOPOISOMERASE-I ENHANCES TFIID-TFIIA COMPLEX ASSEMBLY DURING ACTIVATION OF TRANSCRIPTION, Genes & development, 11(3), 1997, pp. 397-407
The mechanism of coactivation by DNA topoisomerase I(topo I) was exami
ned in a highly defined in vitro transcription system containing Pol I
I and purified factors. Both stimulation of the basal reaction and coa
ctivation occurred dependent on TAF(II)s. Activation was first observe
d at the TFIID-TFIIA stage of initiation and maximal activation requir
ed the concomitant presence of TFIID, TFIIA, topo I, and activator. El
ectrophoretic mobility shift assay demonstrated a dramatic enhancement
in the formation of the TFIID-TFIIA complex by topo I and activator,
dependent on the TAF(II)s. DNase I footprinting confirmed this recruit
ment. A catalytically inactive topo I, which coactivated transcription
, similarly stimulated the rapid formation of the TFIID-TFIIA complex
in the presence of activator. A camptothecin-mediated DNA cleavage ass
ay demonstrated the recruitment of topo I to the template by TFIID. To
po I likely functions during activation by enhancing the formation of
an active TFIID-TFIIA complex on the promoter.