A base substitution (C----T) at position -88 relative to the cap site was identified in the beta-globin gene cloned from an individual with a mild form of beta-thalassemia. This nucleotide change lies in the sequence ACACCC proposed as a distal promoter element. Transient expression of the mutant gene in HeLa cells revealed a modest deficit in beta-globin mRNA production. RNA processing was normal. The -88 beta-thalassemia mutation lends further support for the in vivo role of the distal element in transcription.
