Kvam Erik, Gable Kenneth, Dunn Teresa M, Goldfarb David S
Department of Biology, University of Rochester, Rochester, NY 14627, USA.
Mol Biol Cell. 2005 Sep;16(9):3987-98. doi: 10.1091/mbc.e05-04-0290. Epub 2005 Jun 15.
TSC13 is required for the biosynthesis of very-long-chain fatty acids (VLCFAs) in yeast. Tsc13p is a polytopic endoplasmic reticulum (ER) membrane protein that accumulates at nucleus-vacuole (NV) junctions, which are formed through Velcro-like interactions between Nvj1p in the perinuclear ER and Vac8p on the vacuole membrane. NV junctions mediate piecemeal microautophagy of the nucleus (PMN), during which bleb-like portions of the nucleus are extruded into invaginations of the vacuole membrane and degraded in the vacuole lumen. We report that Tsc13p is sequestered into NV junctions from the peripheral ER through Vac8p-independent interactions with Nvj1p. During nutrient limitation, Tsc13p is incorporated into PMN vesicles in an Nvj1p-dependent manner. The lumenal diameters of PMN blebs and vesicles are significantly reduced in tsc13-1 and tsc13-1 elo3-Delta mutant cells. PMN structures are also smaller in cells treated with cerulenin, an inhibitor of de novo fatty acid synthesis and elongation. The targeting of Tsc13p-GFP into NV junctions is perturbed by cerulenin, suggesting that its binding to Nvj1p depends on the availability of fatty acid substrates. These results indicate that Nvj1p retains and compartmentalizes Tsc13p at NV junctions and that VLCFAs contribute to the normal biogenesis of trilaminar PMN structures in yeast.
TSC13是酵母中极长链脂肪酸（VLCFAs）生物合成所必需的。Tsc13p是一种多跨内质网（ER）膜蛋白，它聚集在核-液泡（NV）交界处，这些交界处是通过核周内质网中的Nvj1p与液泡膜上的Vac8p之间类似拉链的相互作用形成的。NV交界处介导细胞核的逐片微自噬（PMN），在此过程中，细胞核的泡状部分被挤压到液泡膜的内陷中，并在液泡腔中降解。我们报告称，Tsc13p通过与Nvj1p的Vac8p非依赖性相互作用从外周内质网被隔离到NV交界处。在营养限制期间，Tsc13p以Nvj1p依赖性方式被整合到PMN小泡中。在tsc13-1和tsc13-1 elo3-Delta突变细胞中，PMN泡和小泡的管腔直径显著减小。在用新生脂肪酸合成和延长的抑制剂浅蓝菌素处理的细胞中，PMN结构也较小。浅蓝菌素干扰了Tsc13p-GFP靶向到NV交界处，这表明它与Nvj1p的结合取决于脂肪酸底物的可用性。这些结果表明，Nvj1p在NV交界处保留并分隔Tsc13p，并且VLCFAs有助于酵母中三层PMN结构的正常生物发生。
