Fig. 5. p33^ING1b PIP mutants that do not bind PCNA do not induce apoptosis. Hs68 fibroblasts electroporated with constructs encoding GFP plus vector (V), wild-type (WT) or mutant (PM1) versions of p33^ING1b were allowed to recover for 24 hours and the subset indicated were treated with UV. 48 hours after electroporation, cells were harvested and analyzed by FACS (A), following propidium iodide staining to detect sub-G₁ DNA content as a measure of apoptosis. The graph shows the mean ± s.e. from five individual trials. (B) A comparison of results obtained by FACS (examining DNA content) and by TUNEL to confirm FACS results by examining DNA breakage.