A role for Tlg1p in the transport of proteins within the Golgi apparatus of Saccharomyces cerevisiae.
Members of the syntaxin protein family participate in the docking-fusion step of several intracellular vesicular transport events. Tlg1p has been identified as a nonessential protein required for efficient endocytosis as well as the maintenance of normal levels of trans-Golgi network proteins. In this study we independently describe Tlg1p as an essential protein required for cell viability. Depletion of Tlg1p in vivo causes a defect in the transport of the vacuolar protein carboxypeptidase Y through the early Golgi. Temperature-sensitive (ts) mutants of Tlg1p also accumulate the endoplasmic reticulum/cis-Golgi form of carboxypeptidase Y at the nonpermissive temperature (38 degrees C) and exhibit underglycosylation of secreted invertase. Overexpression of Tlg1p complements the growth defect of vti1-11 at the nonpermissive temperature, whereas incomplete complementation was observed with vti1-1, further suggesting a role for Tlg1p in the Golgi apparatus. Overexpression of Sed5p decreases the viability of tlg1 ts mutants compared with wild-type cells, suggesting that tlg1 ts mutants are more susceptible to elevated levels of Sed5p. Tlg1p is able to bind His6-tagged Sec17p (yeast alpha-SNAP) in a dose-dependent manner and enters into a SNARE complex with Vti1p, Tlg2p, and Vps45p. Morphological analyses by electron microscopy reveal that cells depleted of Tlg1p or tlg1 ts mutants incubated at the restrictive temperature accumulate 40- to 50-nm vesicles and experience fragmentation of the vacuole.
Membrane Biology Laboratory, Institute of Molecular and Cell Biology, Singapore 117609, Republic of Singapore.
J G
JG
Coe
A C
AC
Lim
J
J
Xu
W
W
Hong
D000251:Adenosine Triphosphatases; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division; D003001:Cloning, Molecular; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D006026:Glycoside Hydrolases / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D013696:Temperature; D014617:Vacuoles / Q000378:metabolism / Q000648:ultrastructure; D033921:Vesicular Transport Proteins; D043324:beta-Fructofuranosidase
D002352:Carrier Proteins; D005656:Fungal Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; C075137:SEC17 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; C112252:TLG2 protein, S cerevisiae; C107706:VAM3 protein, S cerevisiae; C106736:VTI1 protein, S cerevisiae; D033921:Vesicular Transport Proteins; D006026:Glycoside Hydrolases; D043324:beta-Fructofuranosidase; D000251:Adenosine Triphosphatases; C064404:SEC18 protein, S cerevisiae