Characterization of the mIF4G domains in the RNA surveillance protein Upf2

Thirty percent of all mutations causing human diseases generate mRNAs with premature termination codons (PTCs). Recognition and degradation of these PTC-containing mRNAs is carried out by the mechanism known as nonsense-mediated mRNA decay (NMD). Upf2 is a scaffold protein known to be a central component of the NMD surveillance pathway. It harbors three middle domain of eukaryotic initiation factor 4G (mIF4G) domains in its N-terminal potentially important in regulating the surveillance pathway. In this study, we defined regions within the mIF4G-1 and mIF4G-2 that are required for proper function of NMD and translation termination in Saccharomyces cerevisiae Upf2. In addition, we narrowed down the activity of these regions to an aspartic acid (D59) in mIF4G-1 which is important for NMD activity and translation termination accuracy. Taken together, these studies suggest that inherent charged residues within mIF4G-1 of Upf2 play a role in the regulation of the NMD surveillance mechanism in S. cerevisiae.