Low levels of Ypt protein prenylation cause vesicle polarization defects and thermosensitive growth that can be suppressed by genes involved in cell wall maintenance.
The Rab/Ypt small G proteins are essential for intracellular vesicle trafficking in mammals and yeast. The vesicle-docking process requires that Ypt proteins are located in the vesicle membrane. C-terminal geranylgeranyl anchors mediate the membrane attachment of these proteins. The Rab escort protein (REP) is essential for the recognition of Rab/Ypt small G proteins by geranylgeranyltransferase II (GGTase II) and for their delivery to acceptor membranes. What effect an alteration in the levels of prenylated Rab/Ypt proteins has on vesicle transport or other cellular processes is so far unknown. Here, we report the characterization of a yeast REP mutant, mrs6-2, in which reduced prenylation of Ypt proteins occurs even at the permissive temperature. A shift to the restrictive temperature does not alter exponential growth during the first 3 h. The amount of Sec4p, but not Ypt1p, bound to vesicle membranes is reduced 2.5 h after the shift compared with wild-type or mrs6-2 cells incubated at 25 degrees C. In addition, vesicles fail to be polarized towards the bud and small budded binucleate cells accumulate at this time point. Growth in 1 M sorbitol or overexpression of MLC1, encoding a myosin light chain able to bind the unconventional type V myosin Myo2, or of genes involved in cell wall maintenance, such as SLG1, GFA1 and LRE1, suppresses mrs6-2 thermosensitivity. Our data suggest that, at least at high temperature, a critical minimal level of Ypt protein prenylation is required for maintaining vesicle polarization.
Bialek-Wyrzykowska
U
U
Vienna Biocenter, Institute of Microbiology and Genetics, University of Vienna, A-1030 Vienna, Austria.
Bauer
B E
BE
Wagner
W
W
Kohlwein
S D
SD
Schweyen
R J
RJ
Ragnini
A
A
D048868:Adaptor Proteins, Signal Transducing; D019883:Alkyl and Aryl Transferases; D001483:Base Sequence; D001557:Benzenesulfonates / Q000494:pharmacology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002455:Cell Division / Q000235:genetics; D016764:Cell Polarity; D002473:Cell Wall / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D004271:DNA, Fungal / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing) / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases; D008969:Molecular Sequence Data; D009154:Mutation; D018994:Myosin Light Chains / Q000235:genetics / Q000378:metabolism; D017368:Protein Prenylation; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D013012:Sorbitol / Q000378:metabolism / Q000494:pharmacology; D013489:Suppression, Genetic; D013696:Temperature; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D001557:Benzenesulfonates; D002352:Carrier Proteins; D004271:DNA, Fungal; D005656:Fungal Proteins; C092439:MRS6 protein, S cerevisiae; D008565:Membrane Proteins; D018994:Myosin Light Chains; C490684:SEC6 protein, S cerevisiae; C119383:SLG1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D013012:Sorbitol; C007061:C.I. Fluorescent Brightening Agent 28; D019883:Alkyl and Aryl Transferases; C098848:GFA1 protein, S cerevisiae; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing); D020928:Mitogen-Activated Protein Kinases; C072724:SLT2 protein, S cerevisiae; C060755:YPT1 protein, S cerevisiae; C064320:SEC4 protein, S cerevisiae; D020691:rab GTP-Binding Proteins