Continuous nucleocytoplasmic shuttling of signal transducer and activator of transcription (STAT) proteins is a key to understand their function as cytokine-responsive transcription factors. STATs enter the nucleus both by carrier-dependent and carrier-independent transport pathways, and it was previously shown that STAT1 exits the nucleus only after its prior enzymatic dephosphorylation by nuclear phosphatases. The identification of different transport pathways for unphosphorylated and tyrosine-phosphorylated STAT dimers was made possible by a combination of a diverse set of experimental approaches in the field of molecular biology. In the following, we will summarize some of the techniques that have been successfully used to decipher molecular mechanisms engaged in STAT1 dynamics.
