FIG. 5.

Cell cycle dependency of activity of the RB6K promoter. (A) HeLa cells were transiently cotransfected with the pGL3RB6K-5′- and pSV-β-galactosidase plasmids. Control cotransfections were performed with the pGL3 basic and pGL3CMV plasmids. Twenty-four hours after transfection, cultures were cell cycle arrested for 20 h as described in Materials and Methods. Cells were then harvested, and the distribution of the cells over the stages of the cell cycle was determined by flow cytometry. Bars: white, G₂/M population; black, S population; grey, G₁/G₀ population. (B) In paralel with A, cells were lysed and luciferase and β-galactosidase activities were measured in the lysates. Luciferase values were normalized for β-galactosidase activities and are given relative to luciferase activity measured in G₁/S (hydroxyurea)-arrested cells. Bars: grey, G₁/S (hydroxyurea)-arrested cells; white, G₂/M (nocodazole)-arrested cells.