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Lecture 8

A summary of the Lecture 8 readings complete with diagrams.

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University of Toronto St. George
John Coleman

Lecture 8 Notes Transcription Initiation in Eukaryotes Requires Many Proteins Unlike bacteria, eukaryotes have three different polymerase each with different functions (see table) Bacterial RNA polymerase vs. eukaryotic RNA polymerase II: 1.While bacterial RNA polymerase requires only a single additional protein ( factor) for transcription initiation to occur, eukaryotic RNA polymerases require many additional proteins, collectively called the general transcription factors. 2. Eukaryotic transcription initiation must deal with the packing of DNA into nucleosomes and higher-order forms of chromatin structure, features absent from bacterial chromosomes. RNA Polymerase Requires General Transcription Factors The general transcription factors help to position eukaryotic RNA polymerase correctly at the promoter, aid in pulling apart DNA to begin transcription, and release RNA polymerase from the promoter into the elongation mode once transcription has begunsimilar to the factor in bacterial RNA polymerase The assembly process begins when the general transcription factor TFIID (transcription factor for pol ii) binds to a short double-helical DNA sequence primarily composed of T and A nucleotides TATA boxsequence o The subunit of TFIID that recognizes it is called TBP (for TATA- binding protein). o The TATA box is located 25 nucleotides upstream from the transcription start site. The binding of TFIID causes a large distortion in the DNA which serves as a physical landmark for the promoter. Other factors assemble, along with RNA polymerase II, to form a complete transcription initiation complex. After forming the complex on the promoter DNA, RNA polymerase II must gain access to the template strand at the transcription start point. TFIIH, which contains a
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