Role for Upf2p phosphorylation in Saccharomyces cerevisiae nonsense-mediated mRNA decay

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Nonsense-mediated mRNA decay (NMD) is a critical surveillance pathway that eliminates aberrant mRNAs containing premature termination codons.
• The UPF1 and UPF2 proteins are conserved and essential for NMD, with UPF1 phosphorylation being vital in higher eukaryotes.
• The role of phosphorylation in the NMD pathway of Saccharomyces cerevisiae has been unclear, challenging the universality of this regulatory mechanism.

Purpose of the Study:

• To investigate whether UPF1 and UPF2 proteins in Saccharomyces cerevisiae are subject to phosphorylation.
• To determine the functional significance of Upf2p phosphorylation in the NMD pathway.
• To explore the conserved nature of UPF1 and UPF2 phosphorylation in eukaryotic NMD.

Main Methods:

• In vitro and in vivo biochemical assays were employed to analyze the phosphorylation status of S. cerevisiae Upf1p and Upf2p.
• Interaction studies were performed to assess the effect of Upf2p phosphorylation on its binding to Hrp1p, an essential NMD factor.
• Site-directed mutagenesis was used to identify specific amino acids in Upf2p critical for Hrp1p interaction and NMD function.

Main Results:

• Both S. cerevisiae Upf1p and Upf2p were confirmed to be phosphoproteins.
• Phosphorylation of the N-terminal region of Upf2p was found to be essential for its interaction with the RNA-binding protein Hrp1p.
• Specific phosphorylated serine residues in Upf2p's N-terminal domain were identified as crucial for Hrp1p binding and NMD activity.

Conclusions:

• The phosphorylation of UPF1 and UPF2 is a conserved regulatory mechanism across eukaryotes in the NMD pathway.
• Upf2p phosphorylation plays a critical role in facilitating its interaction with Hrp1p, thereby ensuring efficient NMD.
• This study provides the first evidence that Upf2p phosphorylation is indispensable for the functional execution of NMD.