Biochem 20 - Eukaryotic Transcription

RNA polymerase I

Found in nucleolus, synthesizes precursors of rRNA

RNA polymerase II

Found in nucleoplasm, synthesizes precursors of mRNA

RNA polymerase III

Found in nucleoplasm, synthesizes precursors of tRNA and 5s rRNA

4 elements of RNA polymerase II promoters

1. UP elements (silencers and enhancers) (GC box around -40, CAAT box extending to -110)

2. TATA box at -25 (consensus sequence of TATAA(T/A))

3. Initiator element (lnr) surrounding TSS

4. Downstream regulator/element

Natural promoters consist of core promoter but lack at least 1 of these 4

Preinitiation complex

Made of RNA polymerase II with transcription factors TFII[A-H], controls transcription

Transcription initiation

• Preinitiation complex forms

• Kinases phosphorylate the C-terminal domain of RNA polymerase II — lead to initiation of DNA unwinding, as well as formation of open complex

Mediator complex

Activates/represses transcription; parts are made by MED proteins— tail, middle, and head

Head of mediator complex

Binds to transcription factors

Middle of mediator comples

Binds to C-terminal domain of RNA polymerase II

Tail of mediator complex

Binds to co-activators/repressors bound to enhancer/repressor

Chromatin remodeling complexes

Contain ATP-dependent enzymes that change the formation of nucleosomes and allow for shape to change

Histone modifications

Can activate/repress transcription through modification of the N-terminal; Modifying enzymes attach groups to histone tails to change charges associated to nucleosome