BAK, but not BAX, is constitutively oligomerized in malignant lymphohematopoietic cell lines. (A) Purified BAKΔTM (20 µM) without or with 5 mM DTT was incubated in isotonic buffer containing 1% CHAPS for 1 h and subjected to size exclusion chromatography. (B) Lysates prepared from the indicated log-phase cells in 1% CHAPS were subjected to size exclusion chromatography and blotted with antibodies to BAK (left) or BAX (right). Numbers at the left indicate the sum of the total percentage of BAK that is detected as bound to BCLXL + MCL1 + BCL2 in pull-down assays (“Bound %”) (Fig. 3; Supplemental Fig S5), calculated as described (Dai et al. 2009), and on FPLC assays (running to the left of the dashed line) (“Oligomer %”), calculated as indicated in Supplemental Figure S2. Arrows indicate size markers in kilodaltons. Orange and green boxes indicate cell lines with low (<20%) and high (>55%) constitutive BAK oligomerization, respectively.