Eukaryotic RNA Polymerases Are Not Fully Functional by Themselves

Crude enzyme preparations of RNA polymerases I, II, and III have been shown to be capable of selective transcription 

First we discuss basal transcription factors (fig. 28.12). With all three polymerases, two or more basal transcription factors are required, and some or most of these factors must bind to the promoter before the polymerase can bind. 

Because many eukaryotic genes have been cloned during the last few years, it has become possible to compare the DNA sequences preceding genes that may act as promoterlike signals for RNA polymerase II. One feature that stands out is a common sequence, TATAAA, called the TATA box, found usually 25-30 bp before the transcription start site in many but not all PolII-transcribed genes. 

Phil Sharp and Leonard Guarente showed that at least four transcription factors are required in addition to polymerase II for initiation from the major late promoter of adenovirus. In vitro studies indicate that these factors assemble in an orderly fashion (see fig. 28.12b). First the TFIID complex binds to the TATA box. Sequential binding of TFIIA, TFIIB, RNA polymerase II, and TFIIE follow. It is believed that this multifactor complex functions for a large number of eukaryotic promoters that contain TATA boxes. 

The promoter region for RNA polymerase I also involves the cooperative binding of additional basal transcription factors. In this case two transcription factors bind upstream of the transcription start site (see fig. 28.12a). 

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Eukaryotes Have Three Nuclear RNA Polymerases Eukaryotic RNA Polymerases Are Not Fully Functional by Themselves... 

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