Biology 335 - Molecular Genetics

Eukaryotic Gene Expression

Transcription
Prokaryotes have a single RNA polymerase which is responsible for all transcription.

Eukaryotes have three distinct RNA polymerases, each transcribing a distinct set of RNAs.
RNA Polymerase I

RNA Polymerase II

RNA Polymerase III

 rRNAs

mRNA precursors (hn-RNAs)

small functional RNAs
tRNAs, 5S rRNA, snRNAs, etc...
We will focus the rest of our discussion on RNA Polymerase II as this enzyme is responsible for the synthesis of protein encoding mRNAs...

The process of transcription begins with promoter identification and the initiation of transcription.

In prokaryotes, this is achieved by the interaction of
RNA polymerase core enzyme with a specific initiation factor (sigma factor)
which directs the RNA polymerase to bind the (-35 box), unwind (-10 to +1) and initiation transcription.

In eukaryotes, the process of promoter selection is much more complex...

Like prokaryotes, eukaryotic genes have a promoter sequence located upstream of the initiation of txn
this promoter element has a conserved -TATA- box centered about 35 bp upstream of the initiation site...

This TATA box is the target sequence for a sequence specific DNA binding protein called

TATA-Binding Protein (TBP)

TBP binds to the (-35) TATA box and acts as a nucleation center for the recruitment of

TBP-Associated-Factors (TAFs)
These TAFs are also known as the General RNA Pol II Transcription Factors
(TF II A, B, E, F & H)

Protein-protein interactions between TBP and the TAFs (TF II ___) produces a basal transcription complex
that is competent to interact with RNA polymerase II and direct it to initiate transcription at +1.
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