TFIIIA transcription factor

NHP nonhistone protein TFIIIA transcription factor IIIA... 

Figure 1.6 Design of a polyamide ligand to target the binding site (5 -AGTACT-3 ) of the TFIIIA transcription factor. Panel A Structure of the polyamide ligand. Panel B. Schematic diagram of the binding of the ligand to its target DNA sequence.

Both biochemical and X-ray crystallographic data show that binding of TFIIIA to the 5S rRNA gene internal control region utilizes all but the fourth and sixth of the nine zinc fingers of the transcription factor (Figure 12.15). 

ZnP C2H2 (smart00355) YRCPECGKVEKSKSA LQEHMRTH First identified in the Xenopus transcription factor TFIIIA. Found in numerous nucleic add-binding proteins. Ragl (NP 000439), Strin/ Rfpl38 (NP 057355) 380... 

The first zinc binding motif discovered was that of the eucaryotic transcription factor TFIIIA of Xenopus laevis which contains 9 copies of a Cys2His2-Zinc motif The structure of the binding motif is shown in Fig. 1.4. The central zinc ion serves to pack an a-hehx against a P-sheet and thereby position the a-helix. The recognition of the DNA sequence occurs via this a-helix. 

After TFIIIA binds, proteins TFIIIC and then TFII-IB also bind. Although promoters of classes 2 and 3 do not require TFIIIA, all three classes depend upon TFIIIB and TFIIIC.484 The TATA-binding protein TBF is one of three components present in TFIIIB, which may be regarded as the true initiation factor.47 485 Both TFIIIA and TFIIIC can be described as assembly factors 47 A silkworm RNA pol III has been reported to require a transcription factor consisting of RNA 486... 

Zinc-fingers are common in DNA-binding proteins of eukaryotes but are not found in prokaryotes. Examples of zinc-finger proteins include the RNA polymerase III transcription factor TFIIIA, steroid receptors, and some gene products that control development. The zinc-finger consists of pairs of cysteine and/or histidine residues within an a-helix. These residues bind tightly to a Zn2+ ion, which allows the a-helical amino acids to interact with specific sequences. See Figure 12-18. 

Transcription factor TFIIIA DMA binding and basal transcription... 

This sequence is part of the linear polypeptide chain of the entire protein. The sequence may be repeated one or more times in the DNA-binding protein, and the exact order of the amino acids differs in zinc fingers foimd in different types of DNA-binding proteins. DNA-binding proteins that contain zinc fingers include the transcription factors that bind the respective hormones RAR, RXR, VDR, and THR (Zhu et ah, 1997). Other transcription factors that contain zinc fingers include TFIIIA, Spl (Spl binds to the GC box) (Narayan et ai, 1997), and steroid hormone receptors. 

Aaron Klug discovered the first of the eukaryotic DNA-binding motifs in Xenopus transcription factor IIIA (TFlllA), a protein which binds to the 5S rRNA gene. The resulting complex subsequently binds two other transcription factors and RNA polymerase III, which leads to the initiation of transcription of the 5S rRNA gene. The TFIIIA molecule contains 9 similar 30-residue-long, tandemly repeated modules. Each of these modules contains two invariant Cys residues, two invariant His residues, and several conserved hydrophobic residues (Figure 12.19), and a Zn + ion, which is tetrahedrally coordinated by the invariant Cys and His... 

Three general transcription factors are required for Pol III to Initiate transcription of tRNA and SS-rRNA genes In vitro. Two multimeric factors, TFIIIC and TFIIIB, participate In Initiation at both tRNA and SS-rRNA promoters a third factor, TFIIIA, Is required for initiation at SS-rRNA promoters. As with assembly of Pol I and Pol II Initiation complexes, the Pol III general transcription factors bind to promoter DNA in a defined sequence. 

S Ribosomal RNA genes - The most thoroughly studied genes transcribed by RNA polymerase III are those for 5S ribosomal RNA. At least three protein factors in addition to polymerase III are needed for the expression of the 5S rRNA genes in vitro. Two of these transcription factors (TFIIIB and TFIIIC) appear to participate in the transcription of tRNA genes as well, but one (called TFIIIA) is specific for the 5S genes. 

---