Translation of aberrant mRNAs lacking a termination codon or with a shortened 3'-UTR is repressed after initiation in...

Area of Science:

• Molecular Biology
• Yeast Genetics
• RNA Metabolism

Background:

• Nonstop messenger RNA (mRNA) lacking a termination codon poses a challenge for cellular surveillance.
• Ski7p is a protein hypothesized to recognize stalled ribosomes on nonstop mRNA.

Purpose of the Study:

• To analyze the translation and decay mechanisms of nonstop mRNAs in Saccharomyces cerevisiae.
• To elucidate the role of ribosome stalling and Ski7p in nonstop mRNA metabolism.

Main Methods:

• Analysis of nonstop mRNA abundance and translation products in yeast.
• Investigation of polysome association and ribosome complex formation.
• Assessment of mRNA decay pathways, including the 5' to 3' decay pathway.
• Examination of the impact of Ski7p on nonstop mRNA decay.

Main Results:

• Nonstop mRNAs were associated with polysomes but not Pab1p, indicating translation was initiated.
• Ribosomes translating nonstop mRNA formed stable, heavy polysome complexes, suggesting translation blockage.
• Protein synthesis from nonstop mRNAs was significantly repressed, despite detectable mRNA levels.
• The 5' to 3' decay pathway was accelerated for nonstop mRNA decay in the absence of Ski7p.
• Translation of aberrant mRNAs with shortened 3'-untranslated regions (3'-UTRs) was also repressed.

Conclusions:

• Ribosome stalling at the 3' end of nonstop mRNA likely inhibits further translation, repressing protein synthesis.
• Ski7p influences the decay rate of nonstop mRNA, with its absence accelerating 5' to 3' decay.
• An improper spatial distance between the termination codon and the 3'-UTR leads to translation repression, highlighting the importance of proper mRNA structure.