AID has an intrinsic effect on cell viability. (A) Independently isolated variants of the GC-derived cell lines were assessed for AID levels by Western blotting. A naturally low expressing clone (R1) and high expressing clone (R7) for AID were chosen to look at steady-state apoptotic levels as measured by annexin V binding. R1 cells transgenically expressing AID were also assessed for apoptosis. Statistics represent comparisons between R7 versus R1 and R1-AID and R1. Data are mean ± SD of n = 2 independently cultured clones for each cell line. *P ≤ .05. **P ≤ .01. (B) The AID-negative Ramos 1 clone and 2 AID-high Ramos 7 and 80 clones were assessed for dsDNA break formation by measuring the frequency of stable integration of the pSV2neo E- resistance gene (top panel). These cells were also assessed for DNA uptake by transient transfection with a GFP-expressing plasmid. Statistics represent comparisons between R7 versus R1 and R80 versus R1. Data are mean ± SD of n = 2 or 3 independently cultured clones for each cell line. *P ≤ .05. **P ≤ .01.