Fig. 1. Variations of Jun protein levels during the cell cycle. (A) Co-immunofluorescence microscopy staining of exponentially growing HeLa cells for c-Jun (red), DNA (blue) and JunB (green). (B) Two-dimensional flow cytometry measurement of c-Jun and JunB levels in exponentially growing HeLa cells: FITC fluorescence (arbitrary units) of 10 000 individual cycling cells is plotted against propidium iodide fluorescence (DNA content). G₀/G₁ and G₂/M cells are circled in green and red, respectively. (C) Analysis of c-Jun and JunB proteins in HeLa cells extracts from adherent (Adh) and nocodazole shake-off fractions (M). The percentage of 4n cells is indicated in parentheses. Equal amounts of total cell extracts were separated on SDS–PAGE and immunoprobed with the appropriate antibodies (Lallemand et al., 1997). Densitometry scan quantitation is presented below each gel. (D) Analysis of JunB proteins in different cell types. Equal amounts of extracts from adherent or M phase-enriched human breast cancer cells (MCF7), human cervical carcinoma cells (C33) and mouse fibroblasts (NIH 3T3) were probed for JunB.