Vesicular tubular clusters between the ER and Golgi mediate concentration of soluble secretory proteins by exclusion from COPI-coated vesicles

Cell. 1999 Jul 9;98(1):81-90. doi: 10.1016/S0092-8674(00)80608-X.


We have determined the concentrations of the secretory proteins amylase and chymotrypsinogen and the membrane proteins KDELr and rBet1 in COPII- and COPI-coated pre-Golgi compartments of pancreatic cells by quantitative immunoelectron microscopy. COPII was confined to ER membrane buds and adjacent vesicles. COPI occurred on vesicular tubular clusters (VTCs), Golgi cisternae, the trans-Golgi network, and immature secretory granules. Both secretory proteins exhibited a first, significant concentration step in noncoated segments of VTC tubules and were excluded from COPI-coated tips. By contrast, KDELr and rBet1 showed a first, significant concentration in COPII-coated ER buds and vesicles and were prominently present in COPI-coated tips of VTC tubules. These data suggest an important role of VTCs in soluble cargo concentration by exclusion from COPI-coated domains.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amylases / metabolism*
  • Animals
  • Carrier Proteins / metabolism
  • Chymotrypsinogen / metabolism*
  • Coated Pits, Cell-Membrane / metabolism*
  • Coated Pits, Cell-Membrane / ultrastructure
  • Coatomer Protein
  • Endoplasmic Reticulum / metabolism*
  • Endoplasmic Reticulum / ultrastructure
  • Golgi Apparatus / metabolism*
  • Golgi Apparatus / ultrastructure
  • Male
  • Membrane Proteins / metabolism*
  • Microscopy, Immunoelectron
  • Pancreas / physiology*
  • Pancreas / ultrastructure
  • Phosphoproteins / metabolism
  • Qc-SNARE Proteins
  • Rats
  • Rats, Wistar
  • Receptors, Peptide / metabolism*
  • Saccharomyces cerevisiae Proteins*
  • Vesicular Transport Proteins*


  • BET1 protein, rat
  • Carrier Proteins
  • Coatomer Protein
  • KDEL receptor
  • Membrane Proteins
  • Phosphoproteins
  • Qc-SNARE Proteins
  • Receptors, Peptide
  • SEC31 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Vesicular Transport Proteins
  • Chymotrypsinogen
  • Amylases