Fig. 2. All three stop codons are readthrough in the context of hdc sequences. (A) Schematic drawings of the constructs used to transfect mbn2 cells. The three constructs contain the same part of the hdc cDNA each including a different stop codon. They were expressed under the control of the actin promoter and were tagged at the 5′ end with a Flag epitope and at the 3′ end with the V5 epitope to visualize termination and readthrough products. (B) Western blot from cell extracts probed with FLAG (upper panel) or V5 (lower panel) antibodies. Expression of all three constructs produced two proteins, one termination product (asterisk) and one readthrough product (arrowhead). (C) UGA stop codon is also suppressed in larvae. Western blot probed with the Hdc antibody shows both termination and readthrough (arrow head) products in extracts from wild-type CNS and salivary glands of third instar larvae expressing the wild-type hdc cDNA (20 salivary glands), or a derivative with a stop codon substitution from TAA to TGA (six salivary glands).