Figure 1.

Time course of diffusion for various inert substrates into nuclei. Alexa488-labelled ubiquitin, lactalbumin or MBP as well as GFP were each pre-mixed with Alexa568-labelled thioredoxin. Entry of the substrate pairs into nuclei of permeabilised cells was followed by confocal laser scanning microscopy in separate fluorescence channels. Four time points each are shown. For quantitation see Figure 2. Post-experimental controls show nuclear exclusion of Alexa647-MBP and active import of IBB-GFP (see main text as well as Materials and methods).