Sec61p and BiP directly facilitate polypeptide translocation into the ER.
Secretory proteins are segregated from cytosolic proteins by their translocation into the endoplasmic reticulum (ER). A modified secretory protein trapped during translocation across the ER membrane can be crosslinked to two previously identified proteins, Sec61p and BiP (Kar2p). The dependence of this cross-linking upon proteins and small molecules was examined. Mutations in SEC62 and SEC63 decrease the ability of Sec61p to be cross-linked to the secretory polypeptide trapped in translocation. ATP is also required for interaction of Sec61p with the secretory protein. Three kar2 alleles display defective translocation in vitro. Two of these alleles also decrease the ability of Sec61p to be cross-linked to the secretory protein. The third allele, while exhibiting a severe translocation defect, does not affect the interaction of Sec61p with the secretory protein. These results suggest that Sec61p is directly involved in translocation and that BiP acts at two stages of the translocation cycle.
Sanders
S L
SL
Department of Molecular and Cell Biology, Howard Hughes Medical Research Institute, University of California, Berkeley 94720.
Whitfield
K M
KM
Vogel
J P
JP
Rose
M D
MD
Schekman
R W
RW
D001360:Avidin / Q000737:chemistry; D001483:Base Sequence; D001692:Biological Transport; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D008565:Membrane Proteins / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D010455:Peptides / Q000378:metabolism*; D000069816:SEC Translocation Channels; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins
D005656:Fungal Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C060153:KAR2 protein, yeast; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D010455:Peptides; D000069816:SEC Translocation Channels; C499383:SEC61 protein, S cerevisiae; C074213:SEC62 protein, S cerevisiae; C074215:SEC63 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D001360:Avidin