Figure 2.

Quantitation of passive entry into nuclei. Graphs show evaluations of the time series from Figure 1. Nuclear substrate concentrations are plotted versus time. Each graph shows the indicated diffusion substrate (⧫) and thioredoxin as a control (□). Data points were fitted to c(t)=a+k·t for MBP and GFP, and to c(t)=c_max·(1−e^−k·t) for all other proteins. Averages of analysed cells are shown. Nuclear entry rates depend on the size of these inert substrates. Although nuclear entry of ubiquitin, lactalbumin and thioredoxin occurred rapidly, influx of GFP (27 kDa) was slow and that of MBP (40 kDa) was very slow.