The trans-Golgi network, at the other side of the Golgi stack, is also
Autophagy involves the degradation and recycling within an
a region of interconnected membrane channels engaged in protein
autophagosome of cytoplasmic components that are no longer needed,
sorting. Here, modified proteins processed in the Golgi cisternae are
including organelles. The assembly of the autophagosome involves
packaged selectively into vesicles and dispatched to different parts of
several proteins, including autophagy-related (Atg) proteins, as well as
the cell. The packaging depends on the detection, by the trans-Golgi
Hsc70 chaperone, that translocate the substrate into the lysosome (Boya
network, of particular amino-acid signal sequences, leading to their
et al 2013). Autophagosomes sequester cytoplasmic components and
enclosure in membranes of appropriate composition that will further
then fuse with lysosomes without the participation of a late endosome.
modify their contents, e.g. by extracting water to concentrate them
The 26S proteasome (see below) is also involved in cellular degradation