Half-life of β-actin mRNA in Nalm-6 and CCRF-CEM cells. The CCRF-CEM cells were treated with 5 μM (squares) or 1 μM (circles) Act-D for various times to block mRNA synthesis. Similarly, the Nalm6 cells were treated with 1 μM (lozenges) or 0.5 μM (triangles) Act-D. Total RNA, cDNA, and Real-Time PCR amplification were performed as described in the text. The values represent the mean (±) the standard deviation (SD) of the β-actin RNA copy number per μg of total RNA from three independent experiments. Triplicate determinations were averaged at each data-point. The inset shows the calculated half-life for the β-actin mRNA in each cell line for each treatment.