Protein synthesis by the eukaryotic ribosome represents a significant regulation point during gene expression. We are interested in the mechanisms through which yeast ensure swift, faithful, and appropriate translation, and particularly in those events that occur during translation elongation and termination. In eukaryotes there are three predominant pathways of messenger RNA (mRNA) surveillance that act as quality control mechanisms to ensure defective mRNAs are not translated. These pathways are: 1) No-Go Decay (NGD), where mRNAs may contain a variety of ribosome stalling elements, 2) Non-Stop Decay (NSD), which occurs when an mRNA lacks a termination codon and the ribosome can translate through the poly(A) tail, and 3) Nonsense-Mediated Decay (NMD), where an mRNA contains an aberrant stop codon inside the open reading frame.
To study the regulation of translation in eukaryotes, we have developed a system for monitoring individual steps of translation in a reconstituted system. Using this system, we have examined the basic mechanisms responsible for quality control of translation, regulation of termination, and decay of mRNA transcripts that accumulate stalled ribosomes in the "No-Go" decay pathway. Specifically we have begun to understand the direct role of Dom34 and Hbs1 in promoting ribosome subunit dissociation and peptidyl-tRNA dropoff (Shoemaker et al., Science 2010) as well as the role of these proteins and the ATPase Rli1 in promoting ribosome recycling (Shoemaker et al., PNAS 2012). Currently we are using this system to investigate the mechanisms responsible for quality control in the "Non-stop" and "Nonsense-Mediated" decay pathways. We are interested in how the proteins involved in these surveillance pathways interact with the ribosome and ultimately signal mRNA decay.