Immunoblot analysis and HPLC analysis of [³H]-t-RA binding in nuclear extracts prepared from mock, pSG5/RARα, pSG5/bcr1-PML/RARα and pSG5/bcr3-PML/RARα transiently transfected COS-1 cells. (A) Immunoblot analysis: Nuclear extracts were subjected to 8% polyacrylamide slab gel electrophoresis followed by immunoblotting using the anti-RARα RPα(F ) antibody21 as described in Materials and Methods. (B) Size exclusion HPLC analysis. Nuclear extracts were analyzed as described in the legend of Fig 1. (•) [³H]-t-RA alone; (○) [³H]-t-RA plus 200-fold mol/L excess of unlabeled t-RA. Arrows indicate the elution times of marker proteins (in thousands) used to calibrate the Superose 6 HR 10/30 size exclusion column as indicated in Materials and Methods.