Intranuclear Defect in 9 - Globin mRNA Accumulation Due to a Premature Translation Termination Codon

We have analyzed a cloned #{176}-thalassemia ($#{176}-thal) gene from a patient doubly heterozygous for hemoglobin Lepore and $#{176}-thalassemia. Studies of 3H-uridine incorporation into 9-globin mRNA in this patient’s erythroblasts suggested an intranuclear defect in both $ and Lepore (#{246} ) mRNA synthesis, as did S nuclease analysis of nuclear RNA. However, the nucleotide sequence of the fl#{176}-thal gene revealed only a single base change in codon 39 (CAG -k UAG). which created a premature translation termination codon. The 5’ flanking sequence, including transcription promotor boxes and the mRNA initiation (CAP) site. were normal. The unexpected effect of this mutation on intranuclear fl-mRNA synthesis in vivo was studied by insertion of the cloned gene into a plasmid expression vector and transfection into tissue culture (COS-1 ) cells. fl-Globin mRNA produced by the transfected cells was assessed by S1 nuclease analysis. The $#{176}-39