FIG. 6.

Suppression of BPV-1 amplificational replication by p53 proteins is not the consequence of the p53-induced apoptosis or cell cycle block. (A) Flow cytometric analysis of the cell cycle distribution and the sub-G₁ DNA-containing apoptotic fraction of the p53-transfected CHO4.15 cells. In this assay, 250 ng of the p53 expression constructs without Bcl2 or together with 100 or 250 ng of the Bcl2 expression plasmid pcDBCL2 was transfected into the CHO4.15 cells; 100 ng of BPV-1 full-length origin plasmid pNeoBgl40 was used in each transfection. control, cells with no p53 expression constructs added. Cells were fixed 48 h after transfection. The percentage of apoptotic sub-G₁ DNA-containing signals and the calculated percentages of cells in G₀/G₁, S, and G₂/M phases (from total of 50,000 cells) are indicated on the each graph. y axis, cell number; x axis, DNA content. The sub-G₁ DNA fraction was not considered in the cell cycle calculations. Standard software provided by the manufacturer (Odam-Brucker) was used for the cell cycle calculations. (B) Southern blot analysis of the episomal DNA in the cells cotransfected with p53, Bcl2, and the BPV-1 origin plasmid pNeoBgl40. Episomal DNA was extracted at 72 and 96 h after transfection, digested with HindIII and DpnI, and probed with radiolabeled origin plasmid pUCAlu. Lanes: M, 200 pg of the marker plasmid linearized with HindIII; 1 to 12, transfections 1 to 12 in panel A.