Specific retrieval of the exocytic SNARE Snc1p from early yeast endosomes.
Many endocytosed proteins in yeast travel to the vacuole, but some are recycled to the plasma membrane. We have investigated the recycling of chimeras containing green fluorescent protein (GFP) and the exocytic SNARE Snc1p. GFP-Snc1p moves from the cell surface to internal structures when Golgi function or exocytosis is blocked, suggesting continuous recycling via the Golgi. Internalization is mediated by a conserved cytoplasmic signal, whereas diversion from the vacuolar pathway requires sequences within and adjacent to the transmembrane domain. Delivery from the Golgi to the surface is also influenced by the transmembrane domain, but the requirements are much less specific. Recycling requires the syntaxins Tlg1p and Tlg2p but not Pep12p or proteins such as Vps4p and Vps5p that have been implicated in late endosome-Golgi traffic. Subtle changes to the recycling signal cause GFP-Snc1p to accumulate preferentially in punctate internal structures, although it continues to recycle to the surface. The internal GFP-Snc1p colocalizes with Tlg1p, and immunofluorescence and immunoelectron microscopy reveal structures that contain Tlg1p, Tlg2p, and Kex2p but lack Pep12p and Sec7p. We propose that these represent early endosomes in which sorting of Snc1p and late Golgi proteins occurs, and that transport can occur directly from them to the Golgi apparatus.
Lewis
M J
MJ
Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 2QH, United Kingdom.
Nichols
B J
BJ
Prescianotto-Baschong
C
C
Riezman
H
H
Pelham
H R
HR
D000595:Amino Acid Sequence; D001665:Binding Sites; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism*; D005089:Exocytosis; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins
D005656:Fungal Proteins; D008164:Luminescent Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D011993:Recombinant Fusion Proteins; C083241:SNC1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C112252:TLG2 protein, S cerevisiae; D049452:Green Fluorescent Proteins