RNA polymerase III (POL III) was reported to sense and transcribe cytosolic AT-rich dsDNA into 5'-triphosphate poly(A-U) RNA in human and mouse cells. This dsRNA ligand in turn activated retinoic acid-inducible gene I (RIG-I) leading to production of type I interferon and activation of the transcription factor NF-kappaB (Chiu YH et al. 2009, Ablasser A et al. 2009). Knockdown of POL III expression by siRNA or inhibition of its enzymatic activity by specific chemical inhibitor ML-60218 prevented IFN beta induction in HEK293 cells stimulated with DNA viruses or poly(dA-dT) (Chiu YH et al. 2009, Ablasser A et al. 2009). Moreover, Pol-III inhibition blocked interferon induction by intracellular Legionella pneumophila bacteria [Chiu YH et al 2009].
This project represents cytosolic RNA polymerase III as a complex comprising 17 subunits, although the precise biochemical composition of the cytosolic holoenzyme complex which specifically recognizes AT-rich DNA is not yet known.