Figure 2.

The position of the PTC within the transgene influences NMD, demonstrating a polarity effect. (A) Schematic representation of PTCx, PTCa, and PTCb 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. The positions of nonsense codons within the penultimate exon of the LacZ gene are indicated. (B) Transgenic worms carrying the PTCx and PTCa reporter lack GFP expression (panels i,iii, respectively); however, GFP expression is restored upon SMG-2 depletion (panels ii,iv, respectively). Transgenic worms carrying the PTCb reporter show robust GFP expression (panel v), which is not altered by the inactivation of NMD by SMG-2 depletion (panel vi).