Fig. 2. (A) The abundance of wild-type and UGA-containing LacZ transcripts in the wild-type and upfΔ strains. Total RNAs isolated from the specified strains were separated on a 1% agarose gel and probed with ³²P-labeled LacZ and U3 probes. (B) The nonsense suppression activity in wild-type and upfΔ strains was assessed quantitatively using a β-gal reporter system. The indicated yeast strains were transformed with either a wild-type LacZ gene or a LacZ gene containing the specified nonsense codon. The assays were performed as described in Materials and methods. (C) Nonsense suppression activity in wild type and strains harboring multiple UPF deletions.