Stimulation of ATG12-ATG5 conjugation by ribonucleic acid

Autophagy. Jan-Feb 2007;3(1):10-6. doi: 10.4161/auto.3270. Epub 2007 Jan 27.


The ubiquitin-like conjugation reactions, ATG8/microtubule-associated protein 1 light chain 3/MAP1LC3 (LC3) to phosphatidylethanolamine (PE) and ATG12 to ATG5, are biochemical hallmarks for autophagy, a cellular process that degrades bulk cellular proteins and organelles. The two conjugation reactions share the same E1-like enzyme ATG7 but have different E2-like enzymes, ATG3 for LC3-PE and ATG10 for ATG12-ATG5. In cells, ATG12-ATG5 conjugation appears to be required for LC3-PE conjugation. Previously, in vitro reconstitution of LC3-PE conjugation, but not the upstream ATG12-ATG5 conjugation, was reported. In this study, we describe for the first time the de novo reconstitution of mammalian ATG12-ATG5 conjugation by using purified recombinant proteins. We show that ATG7, ATG10 and ATP as an energy source are all essential for ATG12-ATG5 conjugation, and mutation of the specific lysine residue of ATG5 for ATG12 conjugation abrogates the reaction. Furthermore, a potent stimulating activity for ATG12-ATG5 conjugation was detected in mammalian cell extracts, and was surprisingly identified as ribosomes. Our detail biochemical analyses indicate that the ribonucleic acid (RNA) component of ribosomes is both necessary and sufficient for this stimulation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Autophagy-Related Protein 12
  • Autophagy-Related Protein 5
  • Cell Extracts / chemistry
  • Cell Extracts / pharmacology
  • HeLa Cells
  • Humans
  • Microtubule-Associated Proteins / metabolism*
  • Phosphatidylethanolamines / metabolism
  • Protein Processing, Post-Translational
  • Proteins / metabolism*
  • RNA, Ribosomal / isolation & purification
  • RNA, Ribosomal / pharmacology*
  • Small Ubiquitin-Related Modifier Proteins
  • Spodoptera
  • Ubiquitin-Conjugating Enzymes / metabolism*


  • ATG12 protein, human
  • ATG5 protein, human
  • Autophagy-Related Protein 12
  • Autophagy-Related Protein 5
  • Cell Extracts
  • Microtubule-Associated Proteins
  • Phosphatidylethanolamines
  • Proteins
  • RNA, Ribosomal
  • Small Ubiquitin-Related Modifier Proteins
  • light chain 3, human
  • phosphatidylethanolamine
  • Ubiquitin-Conjugating Enzymes