Eukaryotic
Transciptional Initation/Elongation
Eukaryotic mRNA transcription proceeds as follows:
1. The pre-initiation complex (Figure 28.24) forms.
2. A short region of DNA melts and transcription is intiated.
3. The C-terminal tail of RNA polymerase II becomes strongly phosphorylated and transcription begins, with a helicase unwinding DNA strands ahead of the polymerase complex.
4. A number of the core transcription factors are released and RNA polymerase II, together with TFIIF, moves along the DNA. A residual complex, containing the TATA binding protein (TBP), TFIIA, TATA binding associated factors (TAFs) and probably activator proteins, remains at the start site, ready to initiate another round of transcription.
5. The RNA polymerase II acquires several special elongation factors, some of which assist the enzyme in dealing with pause sites in the DNA. The accessory proteins (which include nucleosome remodeling factors and a specific elongation factor called FACT) also help RNA polymerase II to pass through nucleosomal arrays in in vitro studies.
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