Piecemeal microautophagy of nucleus in Saccharomyces cerevisiae.
Nucleus-vacuole (NV) junctions in Saccharomyces cerevisiae are formed through specific interactions between Vac8p on the vacuole membrane and Nvj1p in the nuclear envelope. Herein, we report that NV junctions in yeast promote piecemeal microautophagy of the nucleus (PMN). During PMN, teardrop-like blebs are pinched from the nucleus, released into the vacuole lumen, and degraded by soluble hydrolases. PMN occurs in rapidly dividing cells but is induced to higher levels by carbon and nitrogen starvation and is under the control of the Tor kinase nutrient-sensing pathway. Confocal and biochemical assays demonstrate that Nvj1p is degraded in a PMN-dependent manner. PMN occurs normally in apg7-delta cells and is, therefore, not dependent on macroautophagy. Transmission electron microscopy reveals that portions of the granular nucleolus are often sequestered into PMN structures. These results introduce a novel mode of selective microautophagy that targets nonessential components of the yeast nucleus for degradation and recycling in the vacuole.
Roberts
Paul
P
Department of Biology, University of Rochester, Rochester, New York 14627, USA.
Moshitch-Moshkovitz
Sharon
S
Kvam
Erik
E
O'Toole
Eileen
E
Winey
Mark
M
Goldfarb
David S
DS
D000071193:Autophagy-Related Protein 7; D002467:Cell Nucleus / Q000378:metabolism*; D006867:Hydrolases / Q000378:metabolism; D008074:Lipoproteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009685:Nuclear Envelope / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D014617:Vacuoles / Q000378:metabolism; D033921:Vesicular Transport Proteins
C114830:ATG7 protein, S cerevisiae; D008074:Lipoproteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D029701:Saccharomyces cerevisiae Proteins; C111373:VAC8 protein, S cerevisiae; D033921:Vesicular Transport Proteins; D006867:Hydrolases; D000071193:Autophagy-Related Protein 7