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Mammalian NSUN2 introduces 5-methylcytidines into mitochondrial tRNAs

Saori Shinoda1, Sho Kitagawa1, Shinichi Nakagawa2

  • 1Department of Chemistry and Biotechnology, Graduate School of Engineering, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.

Nucleic Acids Research
|July 10, 2019
PubMed

Insights

This study identifies 5-methylcytidine (m5C) modifications in mitochondrial tRNAs (mt-tRNAs) and reveals the NSUN2 protein

Area of Science:

  • Mitochondrial biology
  • RNA modifications
  • Molecular genetics

Background:

  • Post-transcriptional modifications of mitochondrial tRNAs (mt-tRNAs) are crucial for mitochondrial protein synthesis and respiratory chain complex assembly.
  • The enzyme NSUN2 is known to modify cytoplasmic tRNAs and mRNAs but its role in mitochondria is unclear.

Purpose of the Study:

  • To investigate the presence and location of 5-methylcytidine (m5C) modifications in mammalian mt-tRNAs.
  • To determine the role of the NSUN2 enzyme in mt-tRNA m5C modification and its mitochondrial localization.

Main Methods:

  • Mass spectrometric analysis to map m5C modifications in mouse and human mt-tRNAs.
  • Analysis of mt-tRNAs from Nsun2 knockout mice and NSUN2 knockout human cells.
  • In vitro reconstitution assays using NSUN2 protein.
  • Structured illumination microscopy to visualize NSUN2 localization.

Main Results:

  • m5C modification was mapped to positions 48-50 in eight mouse and six human mt-tRNAs.
  • m5C was absent in mt-tRNAs from Nsun2 knockout mice and NSUN2 knockout human cells.
  • NSUN2 protein successfully reconstituted m5C at positions 48-50 of mt-tRNA in vitro.
  • Structured illumination microscopy revealed NSUN2 foci within mitochondria, despite its known nuclear localization.

Conclusions:

  • NSUN2 is responsible for m5C modification at positions 48-50 in mammalian mt-tRNAs.
  • NSUN2 localizes to mitochondria, indicating a direct role in mitochondrial RNA metabolism.
  • These findings offer new insights into the physiological and pathological roles of NSUN2 in mitochondrial function.

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