ATA box transcription mutation in β-thalassemia

DNA sequence analysis of a cloned β-globin gene from a Chinese patient with β-thalassemia revealed a single nucleotide substitution (A→G) within the ATA box homology and 28 base pairs upstream from the cap site. The patient was homozygous for this particular allele based on restriction mapping at nine different polymorphic sites in the β-globin gene cluster. Upon transient expression in HeLa cells this gene directed the production of 3-5-fold less β-globin mRNA than the normal β-gene. In RNA isolated from the patient's erythroid cells β-RNA was 10-fold less abundant relative to α-RNA than normal, indicating close approximation of the heterologous cell expression results and the in vivo state. These findings support the validity of such transient expression assays for analysis of phenotypes associated with naturally occurring mutant genes and establish the functional significance of nucleotide substitutions at position -28 for human β-globin gene transcription.