Microautophagy is one of the three common forms of autophagic pathway, but unlike macroautophagy and chaperone-mediated autophagy, it is mediated—in mammals by lysosomal action or in plants and fungi by vacuolar action—by direct engulfment of the cytoplasmic cargo.
Generally a non-selective process, there are three special cases of a selective microautophagic pathway: micropexophagy, piecemeal microautophagy of the nucleus, and micromitophagy, all which are activated only under a specific conditions.
[2] This autophagic pathway engulfs multivesicular bodies formed after endocytosis therefore it plays role in membrane proteins turnover.
[4] 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.
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.