Poster abstracts

Poster number 40 submitted by Carrie Kovalak

The DEAD-box protein Dhh1 promotes decapping by monitoring translocation

Carrie Kovalak (Center for RNA Molecular Biology, Case Western Reserve University), Thomas Sweet (Center for RNA Molecular Biology, Case Western Reserve University), Jeff Coller (Center for RNA Molecular Biology, Case Western Reserve University)

Abstract:
Regulation of the intimately related, conserved processes of mRNA translation and degradation is known to be critical for important processes such as viral infections, early embryogenesis, and control of gene expression by microRNAs. The predominant mRNA decay pathway in Saccharomyces cerevisiae begins with deadenylation followed by decapping, which then allows for 5'-to-3' exonucleolytic digestion of the mRNA. Previous models predicted that Dhh1-like DEAD-box proteins functioned following deadenylation to limit translation initiation and thus lead to ribosome-free mRNA that could be decapped and then degraded. In contrast, recently published work from our lab has established that all three steps of the 5’-to-3’ decay pathway occur while messages are bound by ribosomes. As we now know decay occurs on polyribosome-bound mRNA, we decided to re-evaluate Dhh1’s role in both decay and translational control.

To investigate Dhh1’s functional properties, we utilized the in vivo tethered function assay. We discovered that tethered Dhh1 could repress translation independent of decapping. The presence of tethered Dhh1 saturated a reporter message with ribosomes, indicative of a role for Dhh1 in inhibiting elongation, termination, or ribosome recycling. Further, we find endogenous Dhh1 is part of polyribosome complexes that contain slow-moving ribosomes. These results suggest that limiting translocation is a powerful stimulus for decapping. Consistent with this, when we artificially limited elongation rates by inserting a stretch of rare codons into a translating mRNA, the mRNA is converted into a Dhh1 substrate for decay. Our data collectively indicates that Dhh1 promotes decapping by both recognizing translational elongation aberrancies and limiting a post-initiation step in translation. These findings allude to the existence of an interface between mRNA translation and decay that is controlled by changes in elongation rates monitored by Dhh1-like proteins.

Keywords: decapping, translocation, translational control