 Once activated, the JAKs create docking sites for the STAT transcription factors by phosphorylation of specific tyrosine residues on the cytokine receptor subunits.STATs (signal transduction and activators of transcription) are members of a family of transcription factors, and they have src homology 2 (SH2) domains that allow them to bind to these phosphorylated tyrosine residues.After undergoing JAK-mediated phosphorylation, the STAT transcription factors dimerize, translocate to the nucleus, bind DNA at specific elements and induce expression of specific genes.