Fig. 1. Intracellular accumulation of rhodamine-labelled histone proteins in intact HeLa cells and human lymphocytes: fluorescent microscopy observations. HeLa cells were incubated for 1 hour in the presence of a mixture of rhodamine-labelled histones (2 µM) at 37°C. (A) After fixation by formaldehyde, cells were observed by fluorescent microscopy; (B-H) as in (A) but with the following conditions: (B) cells were incubated at 4°C; (C) incubation was performed in the presence of excess unlabelled histone mixture (x50 mole/mole); cells were pre-incubated for 30 minutes at 37°C before the addition of histones with the following: (D) incubated with NaF (2 mM) (ATP depletion); (E) cytochalasin D (5 µM); (F) BFA (10 µM); (G) nocodazole (20 µM); (H) nystatin (50 µg/ml) and sucrose (0.5 M); (I) as (A), (J) as (G) and (K) as (H) but using confocal microscopy; (L) as (A), (M) as (G) and (N) as (H) but with unfixed cells. (O) Human lymphocytes incubated for 1 hour in the presence of a mixture of rhodamine-labelled histones. All other experimental conditions were as described in Materials and Methods.