domain III/zinc ribbon domain of Transcription Factor IIS
TFIIS is a zinc-containing transcription factor. It has been shown in vitro to have distinct biochemical activities, including binding to RNA polymerases, stimulation of transcript elongation, and activation of a nascent RNA cleavage activity in the RNA polymerase II (Pol II) elongation complex. TFIIS consists of three domains. Domain II and III are sufficient for all known TFIIS activities. Domain III is a zinc ribbon that separated from domain II by a long linker and is indispensable for TFIIS function. The TFIIS homologs, subunits A12.2, B9, and C11, of Pol I, II, and III respectively, are required for RNA cleavage by the polymerases. In a single organism, there are tissue-specific TFIIS related proteins.
Comment:The zinc ribbon is the most conserved part of RPB9, RPC11, RPA12 subunits of RNA polymerases and it is homologous to TFIIS domain III and the C-terminal zinc ribbon domain of archaeal Transcription Factor S. Three antiparallel b-sheets are stabilized by a tetrad of cysteines that chelate zinc
Structure:1Y1V_S, Saccharomyces cerevisiae TFIIS domain III contact with Zn ion at 4.0 A
Jiyao W et al.(2023). "The conserved domain database in 2023.",