FIG. 3.

Linker scanning mutagenesis of the destabilizing 3′UTR region reveals two important elements. The 224-base 3′UTR of GFP-IL-6_Δ2 (Fig. 2) was mutagenized by a linker sequence replacing the natural sequence every 15 bases. Each mutant was stably expressed in COS-7 cells, and the GFP mRNA half-life was assessed by Northern blot hybridization after 30, 60, and 120 min of actinomycin D treatment. The results were normalized to β-actin mRNA expression and are the averages of results from two to four independent experiments. Half-lives were compared to that of GFP-IL-6_wt by the two-tailed Student t test, assuming unequal variances. *, P < 0.05.