The stability of human beta-globin mRNA is dependent on structural determinants positioned within its 3' untranslated region.

Controls that act at both transcriptional and posttranscriptional levels assure that globin genes are highly expressed in developing erythroid cells. The extraordinary stabilities of alpha- and beta-globin mRNAs permit globin proteins to accumulate to substantial levels in these cells, even in the face of physiologic transcriptional silencing. Structural features that determine alpha-globin mRNA stability have recently been identified within its 3'UTR; in contrast, the structural features that determine beta-globin mRNA stability remain obscure. The current study begins to define the structural basis for beta-globin mRNA stability. Two tandem antitermination mutations are introduced into the wild-type human beta-globin gene that permit ribosomes to read into the 3'UTR of the encoded beta-globin mRNA. The readthrough beta-globin mRNA is destabilized in cultured erythroid cells, indicating that, as in human alpha-globin mRNA, an unperturbed 3'UTR is crucial to maintaining mRNA stability. Additional experiments show that the beta-globin and alpha-globin mRNA 3'UTRs provide equivalent levels of stability to a linked beta-globin mRNA coding region, suggesting a parallel in their functions. However, destabilization of the antiterminated beta-globin mRNA is independent of active translation into the 3'UTR, whereas translation into the alpha-globin mRNA 3'UTR destabilizes a linked beta-globin coding region in a translationally dependent manner. This indicates that the alpha- and beta-globin 3'UTRs may stabilize linked mRNAs through distinct mechanisms. Finally, it is shown that neither of the two mutations that, in combination, destabilize the beta-globin mRNA have any effect on beta-globin mRNA stability when present singly, suggesting potential redundancy of stabilizing elements. In sum, the current study shows that a functionally intact beta-globin mRNA 3'UTR is crucial to maintaining beta-globin mRNA stability and provides a level of stability that is functionally equivalent to, although potentially mechanistically distinct from, the previously characterized alpha-globin mRNA 3'UTR stability element.