Figure 1.

A PTCx transgene harboring a nonsense codon is subject to NMD in C. elegans. (A) Schematic representation of GFP/LacZ reporters. Black boxes represent GFP exons, white boxes represent LacZ exons, and gray boxes represent the 3′UTR. Intervening black lines correspond to introns. The natural stop codon is indicated by an asterisk. In the PTCx reporter, the position where a nonsense codon was generated by site-directed mutagenesis is indicated. (B, panel i) Transgenic worms carrying a wild-type reporter show ubiquitous GFP expression. (Panel ii) This expression is not affected by the depletion of SMG-2. Introduction of a nonsense codon (PTCx) resulted in lack of GFP expression (panel iii), whereas inactivation of NMD by SMG-2 RNAi led to strong GFP expression (panel iv). (C) The level of the PTCx reporter mRNA was monitored by semiquantitative RT–PCR. In the PTCx strain, the level of reporter mRNA is very low (lane 3); however, the level of transgene mRNA is significantly increased upon depletion of the smg-2 transcript (lane 5).