Biophysical Journal 84 2

Cover: COS cells transfected with EGFP show that the nucleus remains permeant to the 27 kDa molecule. The red box within the nucleus or the cytoplasm of the cell was photobleached with 488 nm light by single photon confocal scanning. (A) Fluorescence recovery after nuclear photobleaching as EGFP diffuses into the nucleus from the cytoplasm. (B) Cytoplasmic fluorescence recovery after cytoplasmic photobleaching as EGFP diffuses from the nucleus (nuclear fluorescence decreases). (C) Fluorescence recovery after nuclear photobleaching of one nucleus (red box) in a cell containing two nuclei. The second nucleus served as an internal control. See the article by Wei et al. on p. 1317.