High impact information on YPT7

• YPT7 gene disruption did not impair cellular growth at temperatures ranging from 17 degrees C to 37 degrees C. ypt7 null mutants are characterized by highly fragmented vacuoles and differential defects of vacuolar protein transport and maturation [1].
• As Ypt7 is one of many Rab GTPases, ubiquitin-proteasome regulation may be involved in membrane fusion elsewhere [2].
• Accordingly, we propose that the Ccz1-Mon1 complex is critical for the Ypt7-dependent tethering/docking stage leading to the formation of a trans-SNARE complex and subsequent vacuole fusion [3].
• In vitro homotypic fusion of yeast vacuoles occurs in three stages: priming, the Sec18 (NSF)-mediated changes that precede vacuole association; docking, the Ypt7 and SNARE-mediated pairing of vacuoles; and fusion, mediated by calmodulin/V0/t-SNARE interactions [4].
• We propose that the class C-Vps complex both promotes Vps39-dependent nucleotide exchange on Ypt7 and, based on the work of Price et al., acts as a Ypt7 effector that tethers transport vesicles to the vacuole [5].

Biological context of YPT7

• We here report the molecular cloning of a novel GAP-encoding gene (GYP7, for GAP for Ypt7) by high expression from a Saccharomyces cerevisiae genomic library [6].
• Fusion requires Pmk1, Ypt7 - the homologue of a protein involved in S. cerevisiae vacuole fusion - and part of the Sty1 pathway, although Sty1 phosphorylation is unaffected by hypotonic conditions [7].
• We also show that alpha-factor can be degraded in a PEP4-dependent manner in a prevacuolar/endosomal compartment in delta ypt7 cells, providing independent evidence that the pathways of vacuole biogenesis and endocytosis in yeast may intersect in the endosomal membrane system [8].
• It has been demonstrated that Saccharomyces cerevisiae Vam6p/Vps39p plays a critical role in the tethering steps of vacuolar membrane fusion by facilitating guanine nucleotide exchange on small guanosine triphosphatase (GTPase) Vam4p/Ypt7p [9].
• We characterized the fission yeast mutant end4 Delta as well as ypt7 Delta, which is deficient in vacuolar fusion and, hence, endocytosis [10].

Anatomical context of YPT7

• Here we show that mutations in VAM3 (vacuolar t-SNARE) and YPT7 (rab GTPase), which are required to direct protein and membrane delivery from prevacuolar endosomal compartments to the vacuole, dramatically increase/stabilize PtdIns(3)P levels in vivo by disrupting its turnover [11].
• cDNAs representing nine small G protein genes encoding Ypt proteins from the green algae Volvox carteri (YptV) and Chlamydomonas reinhardtii (YptC) were tested for their ability to complement mutations in the YPT1, SEC4, and YPT7 genes of Saccharomyces cerevisiae strains defective in different steps of intracellular vesicle transport [12].
• We report here that endocytosed pheromone alpha-factor accumulates in late endosomes in delta ypt7 cells, indicating that Ypt7p is involved in the regulation of transport steps from late endosomes to the vacuole [8].

Regulatory relationships of YPT7

• In accord with this finding in the reconstituted fusion reaction, the inactivation of Ypt7p by the GTPase-activating protein Gyp1-46p only blocks the fusion of purified vacuoles when Yck3p is present and active [13].

Other interactions of YPT7

• Here we present data indicating that CCZ1 is a close partner of the YPT7 gene, which encodes Rab GTPase and is required for fusion of transport vesicles to vacuole and homotypic vacuole fusion [14].
• In accord with this finding, cells deleted for the gene encoding Ypt7 have normal amounts of Vam7p but have little Vam7p on their isolated vacuoles [15].
• A previous study has shown that a large protein complex containing Vps39 and Vps41 functions as a downstream effector of the active, GTP-bound form of Ypt7, a rab GTPase required for the fusion of vesicular intermediates with the vacuole (Price, A., D. Seals, W. Wickner, and C. Ungermann. 2000. J. Cell Biol. 148:1231-1238) [5].
• In Saccharomyces cerevisiae a protein complex of Mon1 and Ccz1 functions with the small GTPase Ypt7 to mediate vesicle trafficking to the vacuole [16].

References