FRAP analysis of NOL7 nucleolar occupancy demonstrates rapid recovery but low mobility within the nucleolus. (A) The fluorescence recovery within the nucleolus was measured over time for HeLa cells transfected with GFP-tagged NOL7, the high mobility shuttle NCL, and the low mobility resident protein RPS5. Measurements represent thirteen different cells per protein. The curves were fit to the line curve F(t) = F∞(1-eτ·t). (B) The nucleolar occupancy was plotted as a function of recovery versus mobility. The mobile fraction was used as a measurement of free versus complexed protein within the nucleolus and calculated from the regression values in (A) using the formula M
= (F∞-F0)/(Fi-F0). The half-time to maximal recovery was calculated using the formula t1/2 = ln(0.5)/τ and used as a measurement of shuttling between the nucleolus and nucleoplasm. All error bars represent the standard error of the measurement.