Abstract

Archaea are unicellular prokaryotic organisms resembling Bacteria in term of morphology and metabolic diversity but with information processing machineries (transcription, translation, replication) more closely related to those of eukaryotes. RNA polymerase (RNAP) is a large multisubunit enzyme that carry out gene transcription in all living organisms. During transcription, transcript cleavage factor such archaeal TFS and eukaryotic TFIIS enhance the processivity and fidelity of RNAPs. The archaeon Sulfolobus solfataricus has four TFS paralogues. While TFS1 functions as a bona fide cleavage factor, we identified that the paralogous TFS4 evolved into a potent RNA polymerase inhibitor. TFS4 destabilises the TBP–TFB–RNAP pre-initiation complex and inhibits transcription initiation and elongation. All inhibitory activities are dependent on three lysine residues at the tip of the C-terminal zinc ribbon of TFS4; the inhibition likely involves an allosteric component and is mitigated by the basal transcription factor TFEα/β. A chimeric variant of yeast TFIIS and TFS4 inhibits RNAPII transcription, suggesting that the molecular basis of inhibition is conserved between archaea and eukaryotes. TFS4 expression in S. solfataricus is induced in response to infection with the Sulfolobus turreted icosahedral virus. Because archaeal viruses rely exclusively on the transcription machinery of the host cell for the synthesis of viral proteins, expression of TFS4 potentially inhibits virus replication in infected host cells. Our results reveal a compelling functional diversification of cleavage factors in archaea, and provide novel insights into transcription inhibition in the context of the host–virus relationship.