Sge. Roberts et al., A ROLE FOR ACTIVATOR-MEDIATED TFIIB RECRUITMENT IN DIVERSE ASPECTS OFTRANSCRIPTIONAL REGULATION, Current biology, 5(5), 1995, pp. 508-516
Background: Transcription by RNA polymerase II in eukaryotic cells req
uires the ordered assembly of general transcription factors on the pro
moter to form a preinitiation complex. Transcriptional activator prote
ins (activators) stimulate transcription by increasing the rate and/or
extent of preinitiation complex assembly. We have shown previously th
at acidic activators increase the stable association of TFIIB on the p
romoter, a process we refer to as 'recruitment'. In this study, we pro
vide evidence that diverse activators facilitate TFIIB assembly by a r
elated mechanism. We then investigate the activator-mediated assembly
of TFIIB with regard to two aspects of transcription: the distance-dep
endence of activator function, and reinitiation. Results: We have prev
iously described amino-acid-substitution mutants of TFIIB that are abl
e to support an activator-independent basal level of transcription but
do not respond to acidic activators. We now show that these mutants a
lso do not respond to other classes of activators. We demonstrate that
this defect is due to a failure of the activators to recruit the muta
nt TFIIB to the promoter. Activators often lose activity as their dist
ance from the initiation site is increased. We show that this impaired
transcriptional activity correlates with a decrease in TFIIB recruitm
ent. Finally, we find that following the initiation of transcription,
TFIIB dissociates from the promoter, requiring the activator-mediated
reassembly of TFIIB in the preinitiation complex for each new round of
transcription. Conclusion: We have provided evidence that diverse act
ivators recruit TFIIB to the promoter by a related mechanism. This cen
tral step in transcriptional activation is sensitive to promoter archi
tecture, and is required for each new round of transcription.