Relative decay of transiently expressed βζ-chimeric mRNAs in HeLatTAcells. (A) Structures of mRNAs encoded by chimeric βζ-globin genes; regions derived from β- and ζ-globin sequence are indicated in black and white, respectively. The positions of the translation initiation (I) and termination (T) sites, as well as the polyadenylate tail (An), are indicated. The ζ57, ζ57.1-4, ζ49, and ζ65 mutations are illustrated in gray. The 3′UTR of the βζARE mRNA contains a defined 59-nt a denosine/uridine-r ich e lement, inserted 15 nts 3′ to the translation stop codon; this motif destabilizes the full-length transcript, providing an unstable mRNA that is used as a methodological control . RD = relative decay values obtained using the experimental strategy described in Figure 3.