miR-15a blocks K562 cell-cycle progression in G₁. (A) K562 cells were transfected with 100 nM of the indicated microRNA mimics. Forty-eight hours after nucleofection, cells were stained with PI and then analyzed for DNA content by FACS. The population of cells in each phase of the cell cycle was calculated with FlowJo software. Since nucleofection resulted in the death of approximately 30% of K562 cells, the cell-cycle analysis excluded the sub-G₁ population. A representative result of 3 independent experiments is shown. (B) Exogenous c-Myb expression partially overcomes miR-15a-induced cell-cycle arrest. Representative data from 3 independent experiments are shown.