Figure 3.

Quantitative evaluation of an import experiment. (a) From the confocal scans monitoring the import of P4K (Fig. 2 Left), intensity profiles were obtained along a straight line through the center of the nucleus. P4K fluorescence in the extranuclear space (e.s.), the rim, and the intranuclear space can be discriminated clearly. It appears that at the intranuclear side of the nuclear rim, the concentration of P4K rapidly rose to reach, perhaps before the first scan, a constant value amounting to approximately 70% of the extranuclear fluorescence. With time, P4K seemed to fill the intranuclear space from the rim. The intranuclear concentration changes can be described by diffusion into a sphere with zero initial concentration and constant external concentration. (b) The confocal scans monitoring the import of P4K (Fig. 2 Left) were further evaluated for five parameters: (Top to Bottom) the mean fluorescence intensities of the control substrate in the extranuclear medium (open triangles), the mean concentration of the transport substrate in the nuclear rim (filled squares), the mean concentration of the transport substrate in the extranuclear medium (open squares), the mean concentration of the transport substrate in the intranuclear spaces (open circles), and the mean fluorescence intensity of the control substrate in the intranuclear space (open diamonds). In addition, the nuclear radius was measured (not shown) and was found to remain virtually constant over the 30-min time period.