A two-step recognition of signal sequences determines the translocation efficiency of proteins

EMBO J. 1996 Feb 1;15(3):468-78.


The cytosolic and secreted, N-glycosylated, forms of plasminogen activator inhibitor-2 (PAI-2) are generated by facultative translocation. To study the molecular events that result in the bi-topological distribution of proteins, we determined in vitro the capacities of several signal sequences to bind the signal recognition particle (SRP) during targeting, and to promote vectorial transport of murine PAI-2 (mPAI-2). Interestingly, the six signal sequences we compared (mPAI-2 and three mutated derivatives thereof, ovalbumin and preprolactin) were found to have the differential activities in the two events. For example, the mPAI-2 signal sequence first binds SRP with moderate efficiency and secondly promotes the vectorial transport of only a fraction of the SRP-bound nascent chains. Our results provide evidence that the translocation efficiency of proteins can be controlled by the recognition of their signal sequences at two steps: during SRP-mediated targeting and during formation of a committed translocation complex. This second recognition may occur at several time points during the insertion/translocation step. In conclusion, signal sequences have a more complex structure than previously anticipated, allowing for multiple and independent interactions with the translocation machinery.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Biological Transport, Active
  • Chickens
  • DNA / genetics
  • Endoplasmic Reticulum, Rough / metabolism
  • Female
  • Humans
  • In Vitro Techniques
  • Mice
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Ovalbumin / genetics
  • Ovalbumin / metabolism
  • Plasminogen Activator Inhibitor 2 / genetics*
  • Plasminogen Activator Inhibitor 2 / metabolism*
  • Prolactin / genetics
  • Prolactin / metabolism
  • Protein Precursors / genetics
  • Protein Precursors / metabolism
  • Protein Sorting Signals / genetics*
  • Protein Sorting Signals / metabolism*
  • Sequence Homology, Amino Acid
  • Serine Proteinase Inhibitors / genetics*
  • Serine Proteinase Inhibitors / metabolism*
  • Signal Recognition Particle / metabolism


  • Plasminogen Activator Inhibitor 2
  • Protein Precursors
  • Protein Sorting Signals
  • Serine Proteinase Inhibitors
  • Signal Recognition Particle
  • Srp72 protein, mouse
  • preprolactin
  • Prolactin
  • Ovalbumin
  • DNA