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Microautophagy (unlike Macroautophagy and Chaperone-mediated autophagy) is the type of autophagic pathway which is mediated by direct lysosomal (mammals) or vacuolar (plants and fungi) engulfment of the cytoplasmic cargo. Cytoplasmic material is trapped in the lysosome/vacuole by the random process of membrane invagination. Microautophagic pathway is especially important for survival of cells under starvation, nitrogen deprivation or after treatment with rapamycin. Microautophagy generally is a non-selective process but there are 3 special cases of selective microautophagic pathway (micropexophagy, Piecemeal microautophagy of the nucleus, micromitophagy) which are activated under a specific conditions.
Functions of microautophagy
Microautophagy together with macroautophagy is necessary for nutrient recycling under starvation. Microautophagy due to degradation of lipids incorporated into vesicles regulates the composition of lysosomal/vacuolar membrane. Microautophagic pathway functions also as one of the mechanism of glycogen delivery into the lysosomes. This autophagic pathway engulfs multivesicular bodies formed after endocytosis therefore it plays role in membrane proteins turnover. Microautophagy is also connected with organellar size maintenance, composition of biological membranes, cell survival under nitrogen restriction, and the transition pathway from starvation-induced growth arrest to logarithmic growth.
Non-selective microautophagic process can be dissected into 5 distinct steps. Majority of experiments were done on yeast (vacuolar invaginations) but the molecular principles seem to be more general 
Membrane invagination and autophagic tubes formation
Formation of the autophagic tubes is mediated through Atg7-dependent ubiquitin-like conjugation (Ublc) or via vacuolar transporter chaperone (VTC) molecular complex which acts through calmodulin-dependent manner. Calmodulin involvement in tube formation is calcium independent process.
The mechanism of vesicle formation is based on lateral sorting mechanism. Changed composition of membrane molecules (lipid enrichment in the autophagic tubes due to removal of transmembrane proteins) leads spontaneous vesicle formation via phase separation mechanism.
Vesicle expansion and scission
Enlargement of vesicle is mediated by binding enzymes inside of unclosed vesicle. Basically, this process is reversal to endocytosis. Process follows by pich of the vesicle into the lysosomal/vacuolar lumen. This process is independent on SNARE proteins.
Vesicle degradation and recycling
Process of non-selective microautophagy can be observed in all types of eucaryotic cells. On the other hand, selective microautophagy is commonly observed in yeast cells. Three types of selective microautophagy selective microautophagy can be distinguished: micropexophagy, piecemeal microautophagy of the nucleus and micromitophagy 
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