Stable expression of GPI-linked surface proteins does not affect the rate of apoptosis. The PIG-A cDNA sequence was stably introduced as described in Materials and Methods, and apoptosis was measured by annexin V-FITC binding. There was no difference in the rate of apoptosis 24 hours after γ-irradiation between (A) cells stably transfected with PEB versus PEB/PIGA, or (B) cells stably transduced with MN versus MPIN. Background levels of annexin V-FITC binding were higher for JY5 than for granulocytes.