Fig. 5. Instability of newly made nuclear peptides. HeLa cells were permeabilized, allowed to extend nascent peptides in BODIPY-lys-tRNA for 10 minutes in 10 µg/ml MG-132, washed, reincubated in 1 mg/ml cycloheximide for various times, fixed, and confocal sections through the centre of nuclei collected. (A) Cell after initial pulse in BODIPY-lys-tRNA. (B) As A, but after 2 hours chase. Scale bar: 10 µm. (C) Fall in intensity of nuclear and cytoplasmic regions of >50 cells after chases of different times. Lines fit exponential decays; t1/2 of 120 (nucleus) and 690 (cytoplasm) minutes.