Figure 5.

U1 snRNP mobility within the nucleoplasm of living cells. Jump distance distribution for all single U1 snRNPs, which were identified and tracked within the nucleoplasm in the movies acquired at 100 Hz. A minimum number of three diffusion terms was required for an acceptable fit of the data. The largest fraction (long dashes, 77.5%) corresponded to particles, which were immobile. In other words, they performed only a virtual movement caused by the limited localization precision. Here, we obtained a value of σ_immob = 50 nm. These jumps were done by those particles, which were above identified as particles involved in a binding process (Figures 2 and 3). Two particle fractions, f₂ and f₃, corresponded to fast diffusional motion with diffusion coefficients of D₂ = 0.51 ± 0.05 μm²/s (short dashes, 15%) and D₃ = 8.2 ± 3 μm²/s (dotted line, 7.3%). The sum of these fractions yielded an excellent description of the data (full line). The inset shows the same plot with a magnification of the y-scale in order to demonstrate the significant number of large jumps due to particles moving with D₃.