Figure 3.

pX clones are sensitized to p53-mediated apoptosis. (a) Colony regression after exposure to low dosages of the anticancer agent etoposide. pSV-X (2 μg) and pSV-CAT (2 μg) were introduced into NIH 3T3 cells by calcium phosphate coprecipitation and resistant colonies were isolated by selection in G418 as described. Unexpanded pSV-X or pSV-CAT colonies were marked, inspected by microscopy, and photographed 72 hr after treatment with etoposide (Sigma) at the concentration of 0.1 mg/ml. (b) Analysis of chromatin structure (Left and Center) and internucleosomal cleavage of genomic DNA (Right) following treatment with etoposide. Low molecular weight DNA was extracted from equal numbers of cells from either pX or CAT-pooled unexpanded colonies.