The lpr mutation abrogates lamin B cleavage and Raf-1 downregulation in differentiating erythroblasts. Lamin B cleavage and the expression of Raf-1, Fas, and FasL were determined by immunoblotting (A) or by RT-PCR (B). The experiments were repeated 4 times (A) or twice (B) with comparable results. In panel B, the ribonuclease inhibitor (RI) was amplified in parallel reaction as a reference gene.