For example, STAT3 proteins can enter the nucleus by binding to importin α3 and importin α6.[7] On the other hand, STAT1 and STAT2 bind to importin α5.[2] Studies indicate that STAT2 requires a protein called interferon regulatory factor 9 (IRF9) to enter the nucleus.[3] Not as much is known about nuclear entrance of other STATs, but it has been suggested that a sequence of amino acids in the DNA-binding domain of STAT4 might allow nuclear import; also, STAT5 and STAT6 can both bind to importin α3.[6] In addition, STAT3, STAT5 and STAT6 can enter the nucleus even if they are not phosphorylated at tyrosine residues.[6]