Morphologically, the lipophagy in yeast cell mimics microautophagy, which includes a direct amendment of the vacuolar membrane that engulfs lipid droplets (LDs). The molecular mechanism of the membrane modifications that elicits microautophagy still remains elusive. In this study, an analysis of membrane lipid distribution at a nanoscale level showed that PtdIns(4)P is localized in the cytoplasmic leaflet of microautophagic vesicles, which are derived when the vacuole's membrane domains engulfed LDs both in the stationary phase and in acute nitrogen starvation. Furthermore, the PtdIns(4)P-positive raft-like domains engulf LDs through a microautophagic mechanism. When single temperature-conditional mutants of STT4 or PIK1 PtdIns 4-kinases were used, in the vacuole of STT4 and PIK1 mutant cells, microautophagic vesicles drastically decreased at restrictive temperatures, and the labeling density of PtdIns(4)P on the microautophagic vesicles and the sizes of the mutants' microautophagic vesicles also decreased. These results suggest that both Stt4p and Pik1p have important roles in the microautophagy of the vacuole in the stationary phase and under nitrogen starvation conditions.

从形态上讲，酵母细胞中的脂吞噬作用模仿了微自噬作用，其中包括直接吞噬液泡膜的修饰，吞噬了脂滴（LDs）。引起微自噬的膜修饰的分子机制仍然难以捉摸。在这项研究中，在纳米水平上对膜脂质分布的分析表明，PtdIns（4）P位于微自噬囊泡的细胞质小叶中，当自噬泡的膜结构域在固定相和急性氮中吞噬LDs时，PtdIns（4）P定位于此。饥饿。此外，PtdIns（4）P阳性筏状域通过微自噬机制吞噬LD。当使用单一温度条件的STT4或PIK1 PtdIns 4激酶突变体时，在STT4和PIK1突变体细胞的液泡中，在限制温度下，微自噬囊泡急剧减少，微自噬囊泡上PtdIns（4）P的标记密度和突变体微自噬囊泡的大小也减小。这些结果表明，Stt4p和Pik1p在固定相和氮饥饿条件下的液泡微自噬中均具有重要作用。