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Mol. Cell. Biol., Feb 1995, 1049-1059, Vol 15, No. 2
CP George, LM Lira-DeVito, SL Wampler and JT Kadonaga
To explore the diversity in the mechanisms of basal transcription by RNA
polymerase II, we have employed a novel biochemical approach that involves
perturbation of the transcription reaction with exogenously added TFIIB or
TATA box-binding protein (TBP). Under these conditions, we observe
promoter-selective inhibition of transcription by excess TFIIB or excess
TBP. This inhibition occurs at the level of basal transcription, because it
is observed with minimal promoters that comprise only the TATA box and
initiation site sequences as well as with preparations of basal
transcription factors that have been purified to greater than 90%
homogeneity. In addition, the excess basal factors inhibit the assembly of
a functional preinitiation complex but do not inhibit transcription
initiation from preassembled preinitiation complexes. A study of several
promoters revealed a reciprocal trend in the promoter specificity of
inhibition by excess TFIIB versus that by excess TBP. At opposite ends of
this spectrum, promoters are strongly inhibited by excess TFIIB but not
excess TBP and vice versa. These results reveal the existence of a spectrum
of mechanisms for preinitiation complex assembly at different promoters.
The mechanistic preference appears to be specified by the aggregate of
basal promoter elements rather than by an individual component, such as the
TATA box or initiation site sequence. This spectrum provides a new
parameter by which differences in the function of minimal class II
promoters can be analyzed in the context of both basal and regulated
transcription.
Copyright © 1995, American Society for Microbiology
A spectrum of mechanisms for the assembly of the RNA polymerase II transcription preinitiation complex
Department of Biology, University of California, San Diego, La Jolla 92093-0347.
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