A protein complex required for signal-sequence-specific sorting and translocation

Nature. 1994 Aug 11;370(6489):434-40. doi: 10.1038/370434a0.


We have purified a nascent-polypeptide-associated complex (NAC) which prevents short ribosome-associated nascent polypeptides from inappropriate interactions with proteins in the cytosol. NAC binds nascent-polypeptide domains emerging from ribosomes unless a signal peptide is fully exposed. Depletion of cytosolic proteins (including NAC) from ribosomes carrying nascent polypeptides allows the signal recognition particle (SRP) to crosslink to polypeptides irrespective of whether or not they contain signal peptides. In the absence of cytosol, proteins lacking signal peptides can be mistranslocated into the endoplasmic reticulum in vitro, albeit with low efficiency. Readdition of NAC restores the specificity of SRP and fidelity of translocation.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Biological Transport
  • Cattle
  • Cross-Linking Reagents
  • Cytosol / metabolism
  • Endoplasmic Reticulum / metabolism
  • Humans
  • Molecular Sequence Data
  • Peptides / metabolism
  • Protein Binding
  • Protein Biosynthesis
  • Protein Processing, Post-Translational*
  • Protein Sorting Signals / metabolism*
  • Proteins / metabolism*
  • Ribosomes / metabolism
  • Signal Recognition Particle / metabolism


  • Cross-Linking Reagents
  • Peptides
  • Protein Sorting Signals
  • Proteins
  • Signal Recognition Particle