EMSAs of the putative MyoD-binding and mirror repeat sequence in the murine Smtnl1 promoter. [γ-32P]-labeled oligonucleotide probes (3 pmol) were incubated with nuclear extracts isolated from murine skeletal muscle (for MyoD, in A) or A7r5 and HEK293 cells (for mirror repeat sequence (MRS), in B). In some experiments, 200-fold excess unlabeled competitors were added prior to incubation with 32P-labeled probes. For supershift analysis, anti-MyoD antibody (1 μg) was introduced with nuclear extracts following the addition of labeled probe. Results are representative of n = 3 independent experiments.