Membrane recruitment of Aut7p in the autophagy and cytoplasm to vacuole targeting pathways requires Aut1p, Aut2p, and the autophagy conjugation complex
J. Kim et al., Membrane recruitment of Aut7p in the autophagy and cytoplasm to vacuole targeting pathways requires Aut1p, Aut2p, and the autophagy conjugation complex, J CELL BIOL, 152(1), 2001, pp. 51-64
Autophagy is a degradative pathway by which cells sequester nonessential, b
ulk cytosol into double-membrane vesicles (autophagosomes) and deliver them
to the vacuole for recycling. Using this strategy, eukaryotic cells surviv
e periods of nutritional starvation. Under nutrient-rich conditions, autoph
agy machinery is required for the delivery of a resident vacuolar hydrolase
, aminopeptidase I, by the cytoplasm to vacuole targeting (Cvt) pathway. In
both pathways, the vesicle formation process requires the function of the
starvation-induced Aut7 protein, which is recruited from the cytosol to the
forming Cvt vesicles and autophagosomes. The membrane binding of Aut7p rep
resents an early step in vesicle formation. In this study, we identify seve
ral requirements for Aut7p membrane association. After synthesis in the cyt
osol, Aut7p is proteolytically cleaved in an Aut2p-dependent manner. While
this novel processing event is essential for Aut7p membrane binding, Aut7p
must undergo additionalphysical interactions with Aut1p and the autophagy (
Apg) conjugation complex before recruitment to the membrane. Lack of these
interactions results in a cytosolic distribution of Aut7p rather than local
ization to forming Cvt vesicles and autophagosomes. This study assigns a fu
nctional role for the Apg conjugation system as a mediator of Aut7p membran
e recruitment. Further, we demonstrate that Aut1p, which physically interac
ts with components of the Apg conjugation complex and Aut7p, constitutes an
additional factor required for Aut7p membrane recruitment. These findings
define a series of steps that results in the modification of Aut7p and its
subsequent binding to the sequestering transport vesicles of the autophagy
and cytoplasm to vacuole targeting pathways.