δ°‐Thalassemia in cisof βKnossos‐globin gene Normal structure and normal transient expression of the δ‐globin gene

We have previously described the first homozygous cases of Hb Knossos in an Algerian family. The Hb A2was completely absent, ascertaining the presence of a δ°‐thalassemia determinant in cisof the βKnossoss gene. Here, we investigate the affected δ‐globin gene. The complete DNA sequence of the gene and its 5′ and 3′ flanking regions was determined. Only two nucleotide changes were recorded: a C → T substitution at −199 and an AT insertion at −448 upstream from the cap site. To examine the involvement of these changes in gene function, the δ‐gene was subcloned in an expression vector and introduced into COS cells. Analysis of RNA derived from these cells, using an S1protection assay and dot‐blot hybridization, revealed qualitatively and quantitatively normal transcription. The loss of δ‐globin gene activity in vivo may be due to the alteration of a tissue‐specific control.