The structure and activities of the archaeal transcription termination factor Eta detail vulnerabilities of the transcription elongation complex

Transcription elongation complexes (TECs) are normally extremely stable but remain vulnerable to dissociation by domain-specific transcription termination factors. We report the X-ray crystal structure of the superfamily 2 (SF2) helicase Eta (Euryarchaeal termination activity) lacking the nonessential N-terminal domain, one of only two known archaeal-encoded factors capable of disrupting TECs. Eta retains a twin-translocase core domain common to SF2 helicases and a well-conserved C terminus wherein amino acid substitutions can critically abrogate termination activities. Modeling Eta-TEC interactions and the biochemical results obtained with Eta variants add valuable insights into the functional activities of ubiquitously distributed SF2 helicases, highlight areas of susceptibility of TECs to transcription termination factors, and further support a connection between transcription regulation and DNA repair pathways.