The Yeast Decapping Enzyme (Dcp2) Requires its First 234 Amino Acids for Viability in Yeast

Jellisa Ewan (Advisor: Heidi Kaplan, PhD; Offsite Advisor: Ambro van Hoof, PhD)

           In yeast, the major mRNA decay pathway involves deadenylation of the 3’ poly-A tail, followed by decapping of the 5’ m7Gppp cap and subsequent 5’ to 3’ degradation or 3’ to 5’ degradation. This is carried out by Pan2/Pan3 and Ccr4-Not deadenylases, Dcp2 decapping enzyme, and Xrn1 and RNA exosome exoribonucleases, respectively. The eukaryotic mRNA decapping enzyme, Dcp1/2, is essential in yeast, and deletion of either gene is lethal. This lethality can be rescued by suppressor mutations, including mutations in the karyopherin, KAP123, and the Leucine tRNA, TL(GAG)G. These mutations restore viability in dcp2Δ, but do not improve bulk mRNA decay rates. This suggests that Dcp2 essential activity is independent of mRNA decay. Dcp2 possesses a small amino-terminus containing its catalytic domain and a large disordered carboxy-terminus known to facilitate interactions with multiple proteins, including enhancers of decapping (Edc1 and 3). Here, using Saccharomyces cerevisiae as a genetic tool, I examined the essential function of Dcp2 by exploring the functional domains of the protein. Specifically, I investigated the activity of its enzymatic N-terminus, and broader functionality of the protein interacting C-terminus. This study shows that Dcp2 catalytic residues are essential, and that Dcp2 requires its first 234 amino acids for activity. Further investigations are required to determine the function of the extended C-terminus and to understand the mechanisms by which suppressor influence dcpΔ.

Advisory Committee:

• Heidi Kaplan, PhD, Chair
• Ambro van Hoof, PhD, Co-Chair
• Catherine Denicourt, PhD
• Michael Lorenz, PhD
• Kevin Morano, PhD

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