miR-15a can inhibit reporter activity. (A) Schematic representation of the f-luc reporter constructs used. The pBub1/Myb3U plasmid contains the full-length 3′-UTR of the human c-myb fused to f-luc. The promoter of the firefly luciferase (900-bp fragment from Bub1 promoter), stop codon as well as the target sites of the 3 putative microRNAs is also shown. (B) HEK293 T cells were cotransfected with 300 ng pBub1/Myb3U, 15 ng pRL-CMV, and a 50-nM concentration of a given RNA oligonucleotide. Forty-eight hours after transfection, luciferase activities were measured. f-luc activity was normalized to r-luc expression and the mean activities plus or minus SE from 3 independent experiments are shown.