Figure 1.

Autophagy is triggered not only by nitrogen starvation, but also by depletion of sulfur, phosphorus of carbon sources. (A) GFP-Atg8 cleavage is caused by nitrogen, sulfur or phosphorus starvation. MM cultures from the wild-type strain CC10, expressing GFP-Atg8 under the control of the constitutive sty1 promoter from an integrative plasmid, were collected at the logarithmic phase (-) and 4-8-24 h after switching cells to media without nitrogen (w/o N), sulfur (w/o S) or phosphorus (w/o P) sources. Native extracts were analyzed by western blot using anti-GFP antibody. Ponceau staining of the membrane after immuno-detection is shown as a loading control. Numbers below the panels represent the amount of cleaved GFP (quantified as indicated in Materials and Methods) relative to cleaved GFP after 4 h without nitrogen (with an assigned value of 1). (B) GFP-Atg8 cleavage is also induced by glucose exhaustion. The wild-type strain CC10 was grown in standard YE5S (3% glucose) and modified YE5S (1% glucose). Cells were collected at the logarithmic phase and at the indicated times after reaching an OD₆₀₀ of 0.5. For glucose-starvation in YE5S 0.08% of glucose, cells were switched at the logarithmic phase from standard YE5S (3%) to YE5S 0.08%. Samples were treated and analyzed as in (A). Numbers below the panels represent the amount of cleaved GFP relative to the amount after 1 day in standard YE5S (3%) (with an assigned value of 1). (C) Scheme of the different cellular pathways studied in this work, related to sensing and responding to nitrogen and glucose deprivation in fission yeast. See text for details.