Human Cells Require Non-stop Ribosome Rescue Activity in Mitochondria

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• Bacteria utilize trans-translation and rescue factors ArfA and ArfB to hydrolyze peptidyl-tRNA on stalled ribosomes.
• The eukaryotic protein ICT1 shares homology with the bacterial ArfB protein.

Purpose of the Study:

• To investigate the functional similarity and substrate specificity of human ICT1 and bacterial ArfB.
• To determine if ICT1 can functionally replace ArfB in bacterial cells.
• To assess the essentiality of ICT1 in human cells and its role in ribosome rescue.

Main Methods:

• In vitro ribosome rescue assays using human ICT1 and Caulobacter crescentus ArfB.
• Assessing peptidyl-tRNA hydrolysis on ribosomes stalled at different mRNA lengths.
• Complementation assays in C. crescentus lacking trans-translation and ArfB.
• siRNA-mediated silencing of ICT1 in human cells followed by viability assessment.

Main Results:

• Human ICT1 and bacterial ArfB exhibit identical activity and substrate specificity in hydrolyzing peptidyl-tRNA.
• Both proteins effectively rescue ribosomes stalled with short mRNA extensions (≤6 nucleotides) but not longer ones (≥14 nucleotides).
• ICT1 rescues ribosome stalling in C. crescentus lacking its own rescue machinery, and ArfB protects human cells lacking ICT1.

Conclusions:

• Human ICT1 is a functional ribosome rescue factor, interchangeable with bacterial ArfB.
• ICT1 is essential for human cell viability, highlighting the importance of ribosome rescue in eukaryotes.
• Ribosome rescue activity is required in human mitochondria, as indicated by ICT1's essential role.