Heterodimerization of MafG with p45 NF-E2. A NF-E2 DNA-binding site derived from the human PBGD promoter was used as a probe to detect NF-E2 DNA binding activity in nuclear extracts from MEL cells and COS-7 cells transfected with different cDNAs. Competitor oligonucleotides (1 or 15), preimmune serum (PI) or anti-MafG, anti-p45, anti-p18, or anti-ATF4 serum was added to the reaction mix as indicated. Oligonucleotide 1 binds both NF-E2; oligonucleotide 15 contains a single base-pair mutation that blocks NF-E2 binding.16 An arrow indicates the position of NF-E2 and p45/MafG complexes.