Protein Kinase R (PKR), also known as double-stranded RNA-dependent protein kinase, is a key enzyme involved in the innate immune response to viral infections. It is an interferon-induced, serine/threonine protein kinase that becomes activated upon binding to double-stranded RNA (dsRNA), which is often produced during viral replication. Once activated, PKR phosphorylates the eukaryotic initiation factor 2伪 (eIF-2伪), inhibiting protein synthesis and thus limiting viral replication. Additionally, PKR plays roles in regulating apoptosis, cell growth, and differentiation, and has been implicated in cancer and metabolic diseases. Its versatile functions make it a significant target for therapeutic research.