RNA-independent activation of PKR triggers clustering and induces ISR. (A) Quantitative real-time PCR analysis of GADD34 and CHOP levels after forced-dimerization of FKBP-PKR (mean and SEM, N = 5 experiments). (B) Representative immunofluorescence images showing colocalization of FLAG-tagged FKBP-PKR and Edc3. Image crop on right: close-up. Scale bar: 10 µm. (C) Quantification of the number of catalytically dead FKBP-PKR clusters 10 min after dimerizer addition (N = 3 experiments, n > 1,000; **, P < 0.01; ****, P < 0.0001, unpaired Student’s t test, nonparametric).