FACS is a type of flow cytometry, a method for sorting a suspension of biological cells based on specific light scattering and fluorescent characteristics of each cell. We prepared GFP-fused mouse MOR constructs ( Figure 3A) and confirmed that uORFs mediated mouse MOR expression. As shown in Figure 3B, removal of all three uAUGs in cells transfected with pmMUEG #3 resulted in increased fluorescence levels up to 3.5-fold compared to pmMUEG #1 (wild-type). In cells transfected with pmMUEG #2 (only mutated at uAUG#3), the fluorescence level increased up to 1.7-fold compared to pmMUEG #1. These **data** suggest that uORFs of the mouse MOR can be repressed downstream of MOR expression with the most effective repression activity containing uAUG#3. Additionally, these three uAUGs could synergistically repress the downstream of MOR gene expression.