RNase protection assays to assess the :β mRNA ratio in CD34⁺ nucleated erythroblasts and reticulocytes of heterozygotes of the β IVS 2-654 C-T mutation. RNA was extracted from the nucleated erythroblasts of one asymptomatic heterozygote (RH, lane 1) and one normal subject (lane 2). This was compared with reticulocyte RNA of RH (lane 3), the probands LI-1 (lane 4) and LII-3 (lane 5), and another asymptomatic heterozygote control (ST, lane 6). Protected fragments of  and β mRNA, at 97 and 135 bp, are indicated. M represents size marker pBR322 DNA-Msp I. The :β mRNA ratios in lanes 1 to 6 were 1.9, 2.1, 5.5, 5.4, 4.1, and 3.5, respectively. For comparison, :β mRNA ratios in controls were: 1.8 to 2.7 (normals, n = 11); 3.3 to 5.8 (β-thalassemia traits, n = 15), and 4.9, 5.1, and 6.4 (thalassemia intermedias).