Translation of human globin mRNA: globin synthesis in cells containing Hb Leiden

Most structurally abnormal hemoglobins are present in smaller amounts than HbA in the erythrocytes of heterozygous subjects. In the presence of a hemoglobinopathy, alpha and beta globin synthesis remains balanced with equal production of the two types of chains. In reticulocytes of subjects with Hb Leiden (beta 6 or 7 glu leads to 0) there is greater production of alpha than beta globin in vitro (beta/alpha = 0.67), and slightly more beta A is synthesized than beta Leiden (beta A/beta Leiden = 1.28). Differences in specific mRNA content, rates of initiation of chain synthesis, or rates of chain elongation could be responsible for such differential polypeptide synthesis. In the present study, the ribosomal assembly of beta A, beta Leiden, and alpha globin chains was examined in peripheral blood. The translation times of the three chains did not differ significantly (average times: beta A = 65.4 sec, beta Leiden = 70.8 sec, alpha = 53.5 sec). These results indicated that an altered rate of translation was not the source of the anomalous globin synthesis observed in vitro in cells containing Hb Leiden. The experiments suggested that the observed imbalance in alpha/beta production was due to either differential rates of initiation of globin chain synthesis or quantitative differences in the amounts of the specific mRNAs present in the cells.