Transcription factor TFIIIA, zinc finger

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. 

A wide variety of transcription factors contain the zinc finger motif, including the steroid hormone receptors, such as the estrogen and the glucocorticoid receptor. Other transcription factors that contain zinc finger motifs include Spl and polymerase III transcription factor TFIIIA (part of the basal transcription complex), which has nine zinc finger motifs. 

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). 

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. 

The Xenopus 5S RNA gene-specific transcription factor IIIA (TFIIIA) was the first zinc finger protein characterized one decade ago (Klug and Rhodes 1987 Berg 1990 Rhodes and Klug 1993). This protein specifically binds to... 

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