Stimulation of transcript elongation requires both the zinc finger and RNA polymerase II binding domains of human TFIIS.

The eukaryotic transcriptional factor TFIIS enhances transcript elongation by RNA polymerase II. Here we describe two functional domains in the 280 amino acid human TFIIS protein: residues within positions 100-230 are required for binding to polymerase, and residues 230-280, which form a zinc finger, are required in conjunction with the polymerase binding region for transcriptional stimulation. Interestingly, a mutant TFIIS with only the polymerase binding domain actually inhibits transcription, whereas a mutant in which the polymerase binding and zinc finger domains are separated by an octapeptide is only weakly active. The zinc finger itself has no effect on transcription, but in contrast to the wild-type protein, it binds to oligonucleotides. These findings suggest that TFIIS may interact with RNA polymerase II such that the normally masked zinc finger can specifically contact nucleotides in the transcription elongation zone at a position juxtaposed to the polymerization site.