The Interferon-inducible double stranded RNA-dependent protein kinase activator, also known as PKR-associated protein X (RAX in mouse) or PACT (in human) is a cellular protein that heterodimerizes with PKR through its double-stranded RNA binding proteins (dsRBDs). PKR is an interferon (IFN)-induced serine-threonine protein kinase that plays a central role in IFN's antiviral and antiproliferative activities. In the absence of viral infections, PACT activates PKR in response to diverse stress signals as serum starvation and treatments with arsenite or peroxide, resulting in the induction of the apoptotic cascade. PACT is expressed in most cell types at a very low abundance, and overexpression of PACT causes PKR activation, leading to eIF2α phosphorylation. PACT has been shown to interact with another DRBM-containing protein, TRBP (TAR RNA binding protein), and form a triple complex with Dicer to facilitate the production of siRNA.