Relative decay of transiently expressed wild-type and 3′UTR-variant ζ-globin mRNAs in vivo . Values correspond to the quantity of each ζ-globin mRNA remaining after a 16-hr transcriptional chase interval, relative to transiently co-expressed β-globin mRNA. The relative decay of ζWT mRNA was arbitrarily assigned unit value. Each bar represents the mean ± SD value from between two and six replicates. The relative decay of ζARE mRNA, which contains an mRNA-destabilizing element within its 3′UTR [33, 37], was assessed in all experiments as a methodological control. (A) Relative decay of 3′UTR-variant ζ-globin mRNAs carrying octanucleotide mutations. Asterisks indicate p values for each mRNA, relative to ζ57 mRNA (* < 0.02; ** < 0.005; *** < 0.001). (B) Relative decay of 3′UTR-variant ζ-globin mRNAs carrying tetranucleotide mutations in the initial (ζ57.1-4) or terminal (ζ57.5-8) four nucleotides of the nt 57–64 motif (left), or smaller mutations in the first (ζ57.1-2) or second (ζ57.3-4) dinucleotide of this region.