Ribonuclease protection analysis of RNA from MKs and PLTs. Decreasing amounts of RNA from 10 to 2 μg were used for MKs and PLTs. Transfer RNA (tRNA) was used as a negative control to verify specificity of protected fragments. The size of the markers is indicated on the left of the panel. Arrows on the right indicate the position of Mpl (top) and GpIIb (bottom) protected fragments.