Hemoglobin A2: Proteins and Enzymes

The human alpha globin gene cluster located on chromosome 16 spans about 30 kb and includes seven loci: 5'- zeta -pseudozeta - mu - pseudoalpha-1 - alpha-2 - alpha-1 - theta - 3'. The alpha-2 (HBA2) and alpha-1 (HBA1) codingsequences are identical. These genes differ slightly over the 5' untranslated regions and the introns, but theydiffer significantly over the 3' untranslated regions. Two alpha chains plus two beta chains constitute HbA,which in normal adult life comprises about 97% of the total hemoglobin; alpha chains combine with delta chains toconstitute HbA-2, which with HbF (fetal hemoglobin) makes up the remaining 3% of adult hemoglobin. Alpha thalassemiasresult from deletions of each of the alpha genes as well as deletions of both HBA2 and HBA1; some nondeletion alphathalassemias have also been reported. (provided by RefSeq)