title: Bidirectional movement of a nascent polypeptide across microsomal membranes reveals requirements for vectorial translocation of proteins.
abstract: The translocation of polypeptides across the endoplasmic reticulum is a vectorial process that occurs probably through a protein channel by a mechanism as yet undetermined. Here, we demonstrate bidirectional movement of a 221 residue nascent polypeptide across microsomal membranes and provide evidence suggesting that the retrograde movement is through the translocation channel. Retrograde movement is observed only when the polypeptide is generated from a truncated transcript; addition of a stop codon after codon 221 confers vectorial movement. Retrograde movement can also be prevented by glycosylation of the nascent polypeptide, as well as by inclusion of 32 additional amino acids that may promote folding of the translocated chain. We propose that the protein translocation channel is a passive pore that does not create a directional bias in polypeptide movement and that vectorial translocation is driven by nascent chain elongation and sustained by posttranslocation events that prevent retrograde movement.
authors.affiliation: Department of Microbiology, New York University School of Medicine, New York 10016.
authors.forename: C E
authors.initials: CE
authors.lastname: Ooi
authors.forename: J
authors.initials: J
authors.lastname: Weiss
mesh_terms: D000818:Animals; D023181:Antimicrobial Cationic Peptides; D001483:Base Sequence; D001798:Blood Proteins / Q000235:genetics / Q000378:metabolism*; D002474:Cell-Free System; D003062:Codon / Q000235:genetics; D008565:Membrane Proteins; D008566:Membranes / Q000378:metabolism; D008861:Microsomes / Q000378:metabolism*; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000235:genetics; D010446:Peptide Fragments / Q000378:metabolism*; D010539:Permeability; D010957:Plasmids / Q000235:genetics; D014176:Protein Biosynthesis / Q000187:drug effects / Q000502:physiology*; D011499:Protein Processing, Post-Translational / Q000187:drug effects / Q000502:physiology*; D011691:Puromycin / Q000494:pharmacology
chemical_list: D023181:Antimicrobial Cationic Peptides; D001798:Blood Proteins; D003062:Codon; D008565:Membrane Proteins; D009838:Oligodeoxyribonucleotides; D010446:Peptide Fragments; C021623:bactericidal permeability increasing protein; D011691:Puromycin