Figure 2.

mRNA stability is conferred by MS2/Pab1p tethered to the 3′ UTR. (A) The decay of mRNAs in the presence of MS2/Pab1p, analyzed by transcriptional pulse-chase experiments and Northern blotting. The RNA and protein present in each strain is indicated above each group of six lanes, as are the orientation of MS2 sites, and the time (in min) following transcriptional repression. (Vector alone) Strains not expressing a fusion protein, but still transformed with the parental protein vector; (N) not induced sample taken prior to galactose induction. Half-lives are presented at the bottom of each panel. (B) Quantitation of results. Amounts of mRNA were normalized to the level of 18S rRNA, shown below each lane in A. (C) RNA-binding activities of fusion proteins in yeast extracts. Gel retardation analyses were performed with crude extracts of yeast strains containing the proteins indicated at top of each group of lanes. The labeled RNA contains two MS2 coat protein recognition sites. The unlabeled competitor RNAs either contain high (wt) or low (mutant) affinity MS2 recognition sites. Mutant sites bind in vitro with an 100-fold reduction in affinity(Witherell et al. 1991). Black dot is at left of each group of three lanes indicates positions of specific complexes.