The JAK-STAT signaling pathway transmits information from chemical signals outside the cell, through the cell membrane, and into gene promoters on the DNA in the cell nucleus, which causes DNA transcription and activity in the cell. The JAK-STAT system is a major signaling alternative to the second messenger system. JAKs are an integral component of the receptor subunit with very little release or exchange into the cytoplasm and as such are located primarily at the plasma membrane. STAT has seven conserved features: an N-terminal domain (NT), a coiled-coil domain (CC), a central DNA-binding domain (DBD), a linker region, an SH2 domain followed by a single conserved tyrosine residue, and a C-terminal transactivation domain (TAD). JAK phosphorylation of the STAT proteins then results in a spatial reorganisation of the dimer complex, and translocates to the nucleus. Once in the nucleus, STAT dimmers are stabilised by NT:NT interactions and bind cooperatively to tandem sequence elements within promoter regions to activate the transcription of specific gene subsets.