ATA box transcription mutation in β-thalassemia
DNA sequence analysis of a cloned beta-globin gene from a Chinese patient with beta-thalassemia revealed a single nucleotide substitution (A leads to 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 beta-globin gene cluster. Upon transient expression in HeLa cells this gene directed the production of 3-5-fold less beta-globin mRNA than the normal beta-gene. In RNA isolated from the patient's erythroid cells beta-RNA was 10-fold less abundant relative to alpha-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 beta-globin gene transcription.