A potent inhibitor of RNA polymerase (RNAP). Destabilizes the transcription pre-initiation complex of TBP, TFB, DNA and RNAP, inhibits abortive transcription initiation, productive initiation and transcription elongation. Overexpression of TFS1-tip4 (TFS1 with the active tip of this protein, phenocopies this protein) in S.acidocaldarius MW001 leads to severe growth inhibition (PubMed:29203770). May play a role in viral defense (Probable). Binds 2 Zn(2+) ions. Interacts with RNA polymerase; probably competes with TFS1 for the same binding site. At least 4-fold induced following infection by Sulfolobus turreted icosahedral virus 1 (STIV-1) in strain 2-2-12 (PubMed:18337566). Undetected in non-infected cells. Induced following STIV-1 infection, protein is detectable by 12 hours post-infection (p.i.) and increases until at least 24 hours p.i. in strain 2-2-12 (at protein level) (PubMed:29203770). Has 2 zinc-ribbon domains (N-ZR and C-ZR); functionally important residues Lys-76, Lys-77 and Lys-78 are probably located at the tip of a domain that extends from C-ZR into the RNAP active site. The nature of these residues determines if the protein is involved in stalled transcript cleavage and thus activation (Asp and Glu residues in TFS1) or in RNAP inhibition (Lys or Arg residues in this protein TFS4). Increasing numbers of Lys residues lead to an increased ability to inhibit transcription. Strain 2-2-12 is a substrain of P2 that is highly susceptible to infection by Sulfolobus turreted icosahedral virus 1 (STIV-1). Belongs to the archaeal RpoM/eukaryotic RPA12/RPB9/RPC11 RNA polymerase family.