The interferon JAK-STAT pathway

Binding of type I interferons to the IFN-a/ S (type I) receptor results in the phosphorylation and hence activation of two members of the JAK family Tyk2 and JAK 1. These kinases then phosphorylate STAT la (also called STAT 91), STAT (STAT 84) and STAT 2 (STAT 113). 

The three activated STATs disengage from the receptor and bind to the cytoplasmic protein, p48. This entire complex translocates to the nucleus, where it interacts directly with upstream regulatory regions of IFN-sensitive genes. These nucleotide sequences are termed interferon-stimulated response elements (ISREs). This induces/augments expression of specific genes, as discussed later. 

The essential elements of the signal transduction pathway elicited by IFN-y are even more straightforward. IFN-y binding to the type II receptor induces receptor dimerization with consequent activation of JAK1 and JAK2. The JAKs phosphorylate the receptor and subsequently the associated STATla. STATla is then released and forms a homodimer that translocates to the 

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