FIG. 7.

Loss of telomeric overhangs in cells expressing SV40 L-Tg, as shown in the overhang protection analysis of DNA from BJ fibroblasts infected with retrovirus containing SV40 L-Tg at different PD. Cells bypassed senescence at approximately PD 90. DNA was treated with or without Exo I before being analyzed in the overhang protection assay. To verify approximately equal amounts of input DNA, 1/30 of each sample was run on a 0.7% agarose gel and visualized with ethidium bromide (input). (B) Weighted mean sizes of overhangs were quantified and are plotted. Results shown are representative of at least three independent experiments. Error bars represent one standard deviation. (C) Relative amount of overhangs of BJ/L-Tg cells measured by nondenaturing hybridization assay. Undigested whole genomic DNA from BJ at PD 40 and at senescence was first hybridized to the C-rich telomeric probe and then gel fractionated. After the gel was denatured, overhang signals were transferred to a membrane and the gel was rehybridized to the Alu repeat probe. Relative amounts of overhangs were calculated by normalizing signals from the membrane (overhang signals) by the Alu repeat signal (representing total genomic DNA). Results shown are representative of three independent experiments. Error bars represent one standard deviation.