NMD monitors translational fidelity 24/7.

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Nonsense-mediated mRNA decay (NMD) is a conserved eukaryotic surveillance pathway.
• NMD is primarily known for eliminating mRNAs with premature termination codons (PTCs).
• This function prevents the accumulation of potentially toxic truncated proteins.

Purpose of the Study:

• To investigate the full spectrum of NMD substrates.
• To resolve the discrepancy between the known function of NMD and observed NMD targets.
• To propose a revised model for NMD's role in mRNA regulation.

Main Methods:

• High-resolution mRNA profiling in yeast lacking key NMD factors (UPF1, UPF2, UPF3).
• Systematic RNA-Seq and microarray analyses of NMD substrates.
• Ribosomal profiling to assess translation dynamics of NMD targets.

Main Results:

• Approximately 900 NMD substrates were identified in yeast lacking NMD factors.
• The majority of identified NMD substrates lack premature termination codons (PTCs).
• These PTC-lacking NMD targets exhibit increased rates of out-of-frame translation, leading to premature termination.

Conclusions:

• NMD targets extend beyond mRNAs with PTCs.
• Out-of-frame translation and mRNA isoform heterogeneity contribute to NMD substrate recognition.
• NMD functions as a probabilistic quality control pathway throughout the mRNA lifecycle, not solely for PTCs.