Many cytokines, including interferons (IFN), interleukins (IL), and growth factors, induce the transcription of early response genes through the activation of a family of latent transcription factors, STATs~ ignal transducers and activators of transcription)[1-3]. These proteins, which contain src homology 2 (SH2) and SH3 domains, are activated by ligand induced tyrosine phosphorylation which enables them to dimerize and bind to conserved enhancer elements within the promoters of responsive genes [4, 5]. These enhancers are referred to as interferon stimulated response elements (ISRE), gamma interferon activated site (GAS), gamma interferon response region (GRR), and others. Ligand-induced clustering of cytokine receptors results in the tyrosine phosphorylation of one or more chains of the receptor and the activation of STAT proteins. In some instances STATs associate with tyrosine phosphorylated residues in the cytoplasmic domain of the receptor probably through their SH2 domains. Along with STAT activation, the Jak/tyk family of tyro sine kinases are involved in signal transduction [6, 7]. These kinases, tyk2 and Jaks 1-3, are associated with membrane proximal domains of cytokine