Yeast RNA polymerase II subunit RPB9 - Mapping of domains required for transcription elongation

The RPB9 subunit of RNA polymerase II regulates transcription elongation ac tivity and is required for the action of the transcription elongation facto r, TFIIS. RPB9 comprises two zinc ribbon domains joined by a conserved link er region. The C-terminal zinc ribbon is similar in sequence to that found in TFIIS. To elucidate the relationship between the structure and transcrip tion elongation function of RPB9, we initiated a mutagenesis study on the S accharomyces cerevisiae homologue. The individual zinc ribbon domains, in i solation or in combination could not stimulate transcription by a polymeras e lacking RPB9, pol II Delta 9. Mutations in the N-terminal zinc ribbon had little effect on transcription activity. By contrast, mutations in the aci dic loop that connects the second and third beta-strands of the C-terminal zinc ribbon were completely inactive for transcription. Interestingly the a nalogous residues in TFIIS are also critical for elongation activity. A con served charged stretch in the linker region (residues 89-95, DPTLPR) mediat ed the interaction with RNA polymerase II.