Fig. 6.
Fading plots of Lac repressor::GFP foci during dense time sampling. (Upper) Yeast cells are imaged at five successively lower excitation levels, and peak intensities in each 3D stack, normalized to the intensity at the first timepoint, are plotted as a function of time. Photobleaching is visible at both I = I0 and I = 10-1I0. At I = 10-2I0, intensity is seen to increase, which may be due to weak photoactivation of GFP. Lower intensities remain flat for the entire 30s of imaging. (Lower) Fading increases at a given intensity level (I = 10-2I0) as the rate of imaging increases. In total, the samples receive 3.9 s of excitation at 1 Hz, 12 s of excitation at 4 Hz, and 23.7 s of excitation at 10 Hz.