(A) Dissection of coordinates −858 bp to −810 bp containing the LF silencer element into oligomers DM (double module) 1, 2, and 3. Each oligomer (except DM3) contains 2 of the 3 octamer repeats (overlined) that comprise the LF silencer element. (B) UV cross-linking analysis of proteins bound to the DM2 oligomers. DM2 oligomers were [γ-³²P]dATP-labeled and incubated with equal concentrations of nuclear extracts (N.E.), with (+) or without (−) a 100-fold molar excess of unlabeled DM2 oligos, prepared from K562 cells (lanes 2 and 3), uninduced 32Dcl3 cells (lanes 4 and 5), G-CSF–induced 32Dcl3 cells (lanes 6 and 7), MPRO cells (lanes 8 and 9), and MPRO + ATRA cells (lanes 10 and 11). The protein-DNA complexes formed were subjected to UV light at 254 nm for 30 minutes before electrophoresis in a 7.5% SDS-polyacrylamide gel. The position of prestained protein molecular weight markers is indicated. F, unbound probe. Lane 1, probe without nuclear extract.