Info

I W Start of ^transcription

FIGURE 6.21 Eukaryotic Promoter Components—Initiator and TATA Boxes

The promoter for RNA polymerase II has an initiator box at the start site and a TATA box slightly upstream of this. Further upstream there are normally several upstream elements (two are shown here).

FIGURE 6.22 Binding of RNA Polymerase II to Promoter

Starting with TFIID, which contains TATA binding protein, the components of the TFII complex bind one after another. Finally TFIIF helps RNA polymerase II to bind to the DNA.

TATA box

Initiator box

Gene

Startpoint

Gene

Gene

Start of transcription

arrives, accompanied by TFIIF which probably helps RNA polymerase bind (Fig. 6.22). At this point RNA polymerase II can initiate synthesis of RNA. However, it is not yet free to move away from the promoter.

Release of RNA polymerase II from the promoter and elongation of the RNA requires three more TFII complexes, TFIIE, TFIIH and TFIIJ. In particular, TFIIH must phosphorylate the tail of RNA polymerase before it can move (Fig. 6.23). The tail, or CTD (carboxy-terminal domain), consists of a seven-amino acid sequence (Tyr Ser Pro Thr Ser Pro Ser) repeated approximately 50 times. This may be phosphory-lated on the serine or threonine residues. All of the TFII complexes except for TFIIH are left behind as RNA polymerase moves forward.

Like bacterial RNA polymerase, the eukaryotic RNA polymerases all have multiple subunits. RNA polymerase II has more than 10 subunits and shares three of these

CTD (carboxy-terminal domain) Repetitive region at the C-terminus of RNA polymerase II that may be phosphorylated

Upstream Elements Increase the Efficiency of RNA Polymerase II Binding 151

FIGURE 6.23 RNA Polymerase II Moves Forward from the Promoter

Before RNA polymerase II can move forward, the binding of other factors must occur. One of these, TFIIH, phosphorylates the tail of RNA polymerase II. The tail changes position with respect to the body of RNA polymerase II. The other factors leave and RNA polymerase moves along the DNA and begins the process of transcription.

Was this article helpful?

0 0

Post a comment