Binding of nuclear proteins to the DNA motifs. Labeled double-stranded oligonucleotides corresponding to motifs M1–M4 were incubated with nuclear extracts from (A) olfactory epithelium, (B) brain, or (C) liver, as indicated. The Olf-1 binding site (Olf-1s) was used as a positive control. DNA–olfactory epithelium nuclear protein complexes are observed for motifs M1–M4. The DNA–protein interactions are completed by the addition of a 100-fold molar excess of the corresponding unlabeled specific oligonucleotide (A). The positions of the free probes are indicated by filled circles.