Mechanism for recycling tRNAs on stalled ribosomes

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Aberrantly stalled ribosomes trigger ribosome-associated quality control (RQC) and mRNA surveillance.
• The RQC pathway degrades potentially toxic peptides and faulty mRNAs.
• ANKZF1 (yeast Vms1p) is known to release ubiquitinated nascent proteins from 60S ribosomal subunits.

Purpose of the Study:

• To investigate the precise mechanism by which ANKZF1 and Vms1p function within the RQC pathway.
• To elucidate the fate and recycling process of tRNAs released from stalled ribosomes.
• To understand how tRNA integrity is ensured before re-entry into the translation cycle.

Main Methods:

• Utilized a cell-free system to study RQC complex activity.
• Analyzed the cleavage products of polypeptidyl-tRNAs by ANKZF1/Vms1p.
• Investigated the mammalian cytosolic tRNA recycling pathway involving TRNT1.

Main Results:

• Demonstrated that ANKZF1 and Vms1p sever polypeptidyl-tRNAs by cleaving the terminal 3'CCA nucleotides.
• Showed that this cleavage produces a tRNA fragment that requires CCA restoration for aminoacylation.
• Identified a two-step recycling process in the mammalian cytosol involving 2',3'-cyclic phosphate removal and TRNT1-mediated CCA addition.
• Revealed TRNT1's role in discriminating between functional and aberrant tRNAs, targeting the latter for degradation.

Conclusions:

• ANKZF1's precise tRNA cleavage is a critical step in the RQC pathway.
• The tRNA recycling mechanism ensures the integrity of tRNAs before re-entry into translation.
• This quality control ensures the prevention of toxic peptide synthesis and maintains translational fidelity.