TFIIIB functions as a positioning factor, responsible for localizing RNA polymerase correctly. Like SL1 at the pol I promoter, it resembles a sigma factor.
TFIIIA: a zinc finger.
TFIIIB: three subunits.
TFIIIC: at least 5 subunits, >500 kD.
TFIIIA and TFIIIC are assembly factors, whose role is to assist the binding of TFIIIB at the right location.
➢ RNA polymerase III has a internal promoter
Deletion analysis shows that the promoter for 5S RNA genes is internal; initiation occurs a fixed distance (~55 bp) upstream of the promoter.
RNA polymerase III: a minor enzyme activity. in nucleoplasm; tRNAs and other small RNAs (5S rRNA)transcription. inhibited or not by a-amanitin.
All eukaryotic RNA polymerases are large proteins, >500 kD, 8-14 sFra bibliotekbunits.
RNA polymerases II
The largest subunit has a carboxy-terminal domain (CTD), which consists of multiple repeats of a consensus sequence of 7 amino acids. The sequence is unique to RNA polymerase II.
RNA polymerase II: in nucleoplasm , heterogeneous nuclear RNA (hnRNA) transcription (the precursor for mRNA). inhibited by low concentrations of a-amanitin.
Core promoter: ~70 bp.
UBF1: a single polypeptide, it binds to both regions (GC-rich), after which SL1 can bind. RNA pol I then binds to the core promoter. UBF1: SL1: 4 subunits, one subunit--TBP interacts with RNA polymerase. SL1 resembles sigma factor.
Promoter structure of RNA polymerase III
The binding of the assembly factors TFIIIA and TFIIIC, the initiation factor TFIIIB, and RNA polymerase III.
Promoter structure of RNA polymerase III
Chapter 5 . Transcription & RNA Processing in Eukaryotic cells
1. RNA polymerase: 3 types
RNA polymerase I: in nucleolus; rRNA transcription; the most cellular RNA synthesis. Did not inhibited by a-amanitin
➢ Promoter structure of RNA polymerase II
TBP: TATA-binding protein, ~30 kD.
TAFs: for TBP-associated factors.
One upstream promoter, with relatively fixed location.
The RNA polymerase activities of mitochondria and chloroplasts are smaller, and resemble bacterial RNA polymerase.
2. Promoter
➢ RNA polymerase I promoter has two sequence components
TATA box: ~25 bp upstream, 8 bp consensus sequence consists entirely of AT.
The TATA box tends to be surrounded by G C-rich sequences.
It is almost identical with the -10 sequence found in bacterial promoters.
➢ RNA polymerase III has a internal promoter
Promoters for RNA polymerase III consist of bipartite sequences: boxA separated from either boxC or boxB. Or they may consist of separated sequences upstream of the startpoint (Oct, PSE, TATA).