THE IMPORTANCE OF THE 3'-UNTRANSLATED REGION FOR THE EXPRESSION OF THE ALPHA-GLOBIN GENES

With a reverse transcription-polymerase chain reaction procedure, we h ave determined the relative quantities of alpha 2- and alpha 1-mRNA in several patients with heterozygosities for alpha 2- or alpha 1-globin gene mutations, in subjects with two forms of alpha-thalassemia-2 (-3 .7 kb; -4.2 kb), and in two children with an alpha-globin gene triplic ation. Mutations in either one of the two genes do not affect the mRNA production, and the alpha 2- to alpha 1-mRNA ratios in our heterozygo tes are the same (similar to 2.7) as in normal persons with four alpha -globin genes, while the alpha/alpha(X) ratios of similar to 1.7 for a lpha 2 variants and of similar to 6.2 for alpha 1 variants agree with the theoretic values. The deletion of 3.7 kb (leading to the formation of the alpha 2 alpha 1 hybrid gene) and of 4.2 kb (resulting in the p resence of only the alpha 1 gene) causes the alpha 2/alpha 1 ratio to decrease to similar to 1.7, indicating that both are expressed as an a lpha 1 gene. Data obtained for an Hb G-Philadelphia heterozygote (alph a alpha/-alpha G) show that the alpha 2 alpha 1 hybrid gene produces s imilar to 30% less mRNA than an alpha 1-globin gene on a normal chromo some, which may be caused by loss of some sequences 3' to the alpha 2 gene. The same may be the case for the alpha 1-globin gene on the chro mosome with the 4.2 kb alpha-thal-2 deletion. These results suggest an important role for sequences located 3' to the terminating codon in r egulating transcription. Support for this hypothesis was obtained from data for the two children with an alpha-globin gene triplication; the high alpha 2/alpha 1-mRNA ratio can be explained by assuming that the alpha 1 alpha 2 hybrid gene of the alpha 2(alpha 1 alpha 2)alpha 1 tr iplication expresses as an alpha 2 gene.