A fundamental aspect of the biogenesis and function of eukaryotic messenger RNA is the quality control systems that recognize and degrade non-functional mRNAs. Eukaryotic mRNAs where translation termination occurs too soon (nonsense-mediated decay) or fails to occur (non-stop decay) are rapidly degraded. We show that yeast mRNAs with stalls in translation elongation are recognized and targeted for endonucleolytic cleavage, referred to as 'no-go decay'. The cleavage triggered by no-go decay is dependent on translation and involves Dom34p and Hbs1p. Dom34p and Hbs1p are similar to the translation termination factors eRF1 and eRF3 (refs 3, 4), indicating that these proteins might function in recognizing the stalled ribosome and triggering endonucleolytic cleavage. No-go decay provides a mechanism for clearing the cell of stalled translation elongation complexes, which could occur as a result of damaged mRNAs or ribosomes, or as a mechanism of post-transcriptional control.

Eukaryotic cells contain numerous RNA quality-control systems that are important for shaping the transcriptome of eukaryotic cells. These systems not only prevent accumulation of nonfunctional RNAs but also regulate normal mRNAs, repress viral and parasitic RNAs, and potentially contribute to the evolution of new RNAs and hence proteins. These quality-control circuits can be viewed as a series of kinetic competitions between steps in normal RNA biogenesis or function and RNA degradation pathways. These RNA quality-control circuits depend on specific adaptor proteins that target aberrant RNAs for degradation as well as the coupling of individual steps in mRNA biogenesis and function.

Eukaryotic mRNAs are subject to quality control mechanisms that degrade defective mRNAs. In yeast, mRNAs with stalls in translation elongation are targeted for endonucleolytic cleavage by No-Go decay (NGD). The cleavage triggered by No-Go decay is dependent on Dom34p and Hbs1p, and Dom34 has been proposed to be the endonuclease responsible for mRNA cleavage. We created several Dom34 mutants and examined their effects on NGD in yeast. We identified mutations in several loops of the Dom34 structure that affect NGD. In contrast, mutations inactivating the proposed nuclease domain do not affect NGD in vivo. Moreover, we observed that overexpression of the Rps30a protein, a high copy suppressor of dom34Delta cold sensitivity, can restore some mRNA cleavage in a dom34Delta strain. These results identify important functional regions of Dom34 and suggest that the proposed endonuclease activity of Dom34 is not required for mRNA cleavage in NGD. We also provide evidence that the process of NGD is conserved in insect cells. On the basis of these results and the process of translation termination, we suggest a multistep model for the process of NGD.