In untreated cells STAT1 and STAT3 are distributed diffusely in the cytoplasm and nucleus. A few minutes after Interleukin-6 treatment both are preferentially located in the nucleus. This translocation is transient; after 2 hours the distribution is comparable to that of untreated cells (Zhang et al. 1995). It is believed that STATs entry to the nucleus is mediated by importins via nuclear pore complexes (NPCs) (Reich & Liu 2006).