A Novel C to A Substitution in the CCAAT Box of beta Globin Gene.

The promoter of the human beta-globin gene contains three positive cis-acting elements required for maximal transcription: the CACCC box located between −86 and −90, the CCAAT box located between −72 and − 76 and the TATA box located between −28 and −31 relative to the start site of transcription. Naturally occurring mutations within the TATA and the CACCC box regions have been recorded in patients with beta⁺ thalassemia. Mutations within the TATA box disrupt assembly of the basal transcription complex, while mutations at the CACCC box prevent binding of an erythroid-specific transcription factor EKLF. Surprisingly, no mutations have so far been identified in the highly conserved element CCAAT box and the transcription factors responsible for the regulatory activity of the CCAAT site in vivo have been less intensively studied. We report a novel mutation −76 C>A (HBB c. −126) detected by sequencing analysis of beta globin gene in a Italian beta⁺ thalassemic patient. The transversion C>A hits the first nucleotide in the CCAAT box of the beta globin gene. The carrier, a male 44 years old, shows a mild hypochromic and microcytic anaemia with reduced mean corpuscular volume and mean corpuscular haemoglobin (MCV 75 fl, MCH 25 pg) and Hb A2 level slightly increased (3.9%). Recently, studies in vitro in gel-shift and reporter assays, investigating the transcriptional activity of human beta globin CCAAT box, have identified five factors: NF-Y (CP1) a ubiquitous CCAAT box binding complex, GATA-1 an erythroid-specific transcription factor, C/EBPbeta, C/EBPgamma and C/EBPdelta members of CCAAT/enhancer-binding protein family involved in hemapoietic regulation. This represents the first report of a natural mutation of the human beta-globin CCAAT box and confirms its functional significance for in vivo transcription.