Time-courses of the original and labeled system. At t = 0, all STAT molecules are labeled and the original system (solid blue) coincides with the labeled one (dashed red). After the initial signal wave, STAT molecules return from the nucleus to the cytoplasm. Since the label transit-time for a complete cycle of cytoplasmic STAT is investigated, the returning molecules release their label, which is counted in an artificial entity (bottom right, green). Unlabeled molecules are depicted in yellow. Solid rose lines depict half labeled species, i.e. dimers of a labeled and an unlabeled molecule. They are shown only once, since the trajectory for example of pSL-pSF is identical to the one of pSF-pSL.