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Among all the organelles in an animal cell, only mitochondria have their own independent genomes. Animal mitochondrial DNA is a double-stranded, closed-circular molecule with around 20,000 base pairs. Mitochondrial DNA is unique in that one of its two strands, the heavy, or H, -strand is guanine rich, whereas the complementary strand is cytosine rich and called the light, or L, -strand. Compared to nuclear DNA, mitochondrial DNA has a very low percentage of non-coding regions and is marked by...
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Mitochondrial presequences harbor variable strengths to maintain organellar function.

Youmian Yan1, Baigalmaa Erdenepurev1, Thiago N Menezes1

  • 1Department of Biochemistry & Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA.

The Journal of Cell Biology
|January 8, 2026
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Summary
This summary is machine-generated.

Mitochondrial protein presequences vary in strength, impacting import efficiency and cellular fitness. This study quantifies presequence strength, revealing its broader role beyond stress signaling in maintaining organellar homeostasis.

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Area of Science:

  • Cell Biology
  • Mitochondrial Biology
  • Protein Import

Background:

  • Mitochondrial proteins require N-terminal presequences for targeting and import.
  • Presequences are generally amphiphilic helices but lack a consensus motif, leading to variable import efficiencies.
  • The concept of 'presequence strength' is used in models like stress sensing, but quantitative analysis is lacking.

Purpose of the Study:

  • To quantitatively define multiple aspects of presequence strength.
  • To investigate the impact of presequence strength on mitochondrial function and cellular fitness.
  • To explore the broader implications of presequence strength variability in biological processes.

Main Methods:

  • Utilized the MitoLuc protein import assay to measure presequence strength.
  • Assessed differential import efficiencies during mitochondrial uncoupling.
  • Evaluated the rescue of respiratory growth defects in complex IV-deficient yeast.

Main Results:

  • Identified variable import efficiencies among presequences, including those regulating the mitochondrial unfolded protein response (UPRmt).
  • Demonstrated that presequence strength significantly influences mitochondrial function and cellular fitness, extending beyond stress signaling.
  • Showed that only robust presequences fully rescued respiratory growth defects, linking presequence strength to metabolic potential.

Conclusions:

  • Presequence strength is a multifaceted characteristic, encompassing total imported protein, maximal import velocity, and sensitivity to uncoupling.
  • Annotation of presequences as weak or strong requires more nuanced characterization.
  • Variability in presequence strength plays a meaningful role in cellular fitness and organellar homeostasis, suggesting broad biological exploitation.