Fig. 5: Converging degrons couple stress resolution to stress response silencing and cell survival.

a, Degradation of WT-swap or degron/MTS-swap HRI reporters was monitored by flow cytometry. Similar results in n = 2 independent experiments b, The HRI helix 2 and the helical cDELE1 degron were fused in front of GFP, and localization was monitored by microscopy. Scale bar, 5 μm. Similar results in n = 3 independent experiments. c, The HRI helix 2 degron mediates import of citrate synthase (CS), as determined by flow cytometry. Experiment performed once and validated by microscopy. d, Autoradiography image of SIFI-dependent ubiquitylation of HRI(1–138)–SUMO in the presence of increasing concentration of presequence. Similar results in n = 2 independent experiments. e, Flow cytometry analysis of HRI stability in WT and ΔUBR4 cells depleted of TIMM8A and TIMM8B. Similar results in n = 2 independent experiments. f, Overexpression of mitochondrial precursors induces ISR signalling that depends on presequences and restricted by UBR4, as monitored through the uORF-ATF4 reporter. Similar results in n = 2 independent experiments. g, DELE1 or HRI depletion rescues synthetic lethality after loss of UBR4 and TIMM8A. h, ISRIB rescues the synthetic lethality after loss of UBR4 and mitochondrial import or ETC assembly factors. Some competitions were performed at the same time as experiments for Fig. 1c and some controls are therefore reshown. i, Model of regulated stress response silencing by the E3 ligase SIFI. For gel source data, see Supplementary Fig. 1.