Four translation initiation pathways employed by the leaderless mRNA in eukaryotes.

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Leaderless mRNAs lack 5' untranslated regions, remnants of ancient translation initiation.
• They constitute a significant portion of the transcriptome in various species, including eukaryotes.
• In prokaryotes, leaderless mRNAs initiate translation via 70S ribosomes without protein factors.

Purpose of the Study:

• To investigate the translation initiation mechanisms of leaderless mRNAs in mammalian cells.
• To explore alternative pathways beyond canonical eukaryotic initiation factors.

Main Methods:

• Utilized the Fleeting mRNA Transfection technique (FLERT).
• Assessed translation of a leaderless reporter mRNA under inactivated eukaryotic initiation factor conditions (eIF2 and eIF4F).

Main Results:

• Leaderless mRNA translation is resistant to inactivation of key eukaryotic initiation factors eIF2 and eIF4F.
• Identified an unconventional, bacterial-like eIF5B/IF2-assisted translation initiation pathway.
• This pathway is similar to that used by hepatitis C virus-like internal ribosome entry sites (IRESs).

Conclusions:

• Leaderless mRNAs can employ at least four distinct translation initiation pathways in eukaryotes.
• This finding expands our understanding of mRNA translation and gene expression regulation.