miR-15a interacts with the 3′-UTR of c-myb directly. (A) Dose-dependent inhibition of luciferase activity by miR-15a. HEK293 T cells were cotransfected with 200 ng pBub1/Myb3U, 10 ng pRL-CMV, and either miR-Control or miR-15a at the concentrations indicated, and relative luciferase activities were calculated as described above. The mean activities plus or minus SE from 3 independent transfection experiments are shown. (B) Constructs for the wild type c-myb UTR reporter and miR-15a seed binding sites (bold) deletion mutants. Only the miR-15a binding regions are shown. (C) Deletion of the seed binding sites of miR-15a in 3′-UTR of c-myb reduces miR-15a activity. HEK293 T cells were cotransfected with 10 ng pRL-CMV, 50 nM miR-15a or miR control and 4 3′-UTR of c-myb containing reporter constructs (300 ng), respectively. miR-15a inhibition activity was calculated as a function of luciferase activity reduction by miR-15a relative to miR control. Data are representative of 3 independent experiments.