Ubiquitin-like modifier involved in autophagosome formation. Whereas LC3s are involved in elongation of the phagophore membrane, the GABARAP/GATE-16 subfamily is essential for a later stage in autophagosome maturation (By similarity). Interacts with GABRG2 and beta-tubulin. Ubiquitous. Expressed at very high levels in the brain, heart, peripheral blood leukocytes, liver, kidney, placenta and skeletal muscle. Expressed at very low levels in thymus and small intestine. The precursor molecule is cleaved by ATG4B to form the cytosolic form, GABARAPL3-I. This is activated by APG7L/ATG7, transferred to ATG3 and conjugated to phospholipid to form the membrane-bound form, GABARAPL3-II. ATG4B also mediates the delipidation required for GABARAPL1 recycling when autophagosomes fuse with lysosomes (By similarity). Belongs to the ATG8 family.