Figure 3A, B, C. Cell lysates of HEK293 cells co-transfected with FLAG-FIP200 (A) and either empty vector control, Myc-C9orf72S or Myc-C9orf72L were subjected to immunoprecipitation with anti-Myc (A and B) antibodies. Immune pellets were probed for Myc-C9orf72 (A and B), FLAG-FIP200 (A) on immunoblots. A, B, C. Cell lysates of HEK293 cells co-transfected with HA-ULK1 (B) and either empty vector control, Myc-C9orf72S or Myc-C9orf72L were subjected to immunoprecipitation with anti-Myc (A and B) antibodies. Immune pellets were probed for Myc-C9orf72 (A and B), HA-ULK1 (B) on immunoblots. A, B, C. Cell lysates of HEK293 cells co-transfected with Myc-ATG13 (C) and either empty vector control, FLAG-C9orf72S or FLAG-C9orf72L were subjected to immunoprecipitation with anti-FLAG (C) antibodies. Immune pellets were probed for FLAG-C9orf72 (C), Myc-ATG13 (C) on immunoblots. D, E. Cell lysates of HEK293 cells transfected with empty vector control, Myc-C9orf72S or Myc-C9orf72L were subjected to immunoprecipitation with anti-Myc antibodies Immune pellets were probed for Myc-C9orf72 and endogenous FIP200, ULK1, and ATG13. There are multiple alternatively spliced forms of ATG13 (Jung et al., 2009; Alers et al., 2011); ATG13* is most likely a smaller alternative spliced form of ATG13 that is enriched by interaction with C9orf72. F, G, H. HeLa cells transfected with Flag-FIP200 and Myc-C9orf72 were fixed and processed for PLA analysis. Transfections were laced with mVenus to enable identification of transfected cells for analysis where required (green). PLA signals (red) were counted per cell (Mean ± SEM; one-way ANOVA with Fisher's LSD test, **** P ≤ 0.0001; N (cells) = (F) C9orf72S: 22; C9orf72L: 18; EV+FIP200: 18; C9orf72S+FIP200: 18; C9orf72L+FIP200: 17. Scale bar = 10 µm; see also Fig EV2. F, G, H. HeLa cells transfected with HA-ULK1 and Myc-C9orf72 were fixed and processed for PLA analysis. Transfections were laced with mVenus to enable identification of transfected cells for analysis where required (green). PLA signals (red) were counted per cell (Mean ± SEM; one-way ANOVA with Fisher's LSD test, **** P ≤ 0.0001; N (cells) = (G) C9orf72S: 21; C9orf72L: 20; EV+ULK1: 20; C9orf72S+ULK1: 22; C9orf72L+ULK1: 20. Scale bar = 10 µm; see also Fig EV2. F, G, H. HeLa cells transfected with Myc-ATG13 and EGFP-C9orf72 were fixed and processed for PLA analysis. Transfections were laced with mVenus to enable identification of transfected cells for analysis where required (green). PLA signals (red) were counted per cell (Mean ± SEM; one-way ANOVA with Fisher's LSD test, **** P ≤ 0.0001; N (cells) = (H) C9orf72S: 11; C9orf72L: 10; EV+ ATG13: 11; C9orf72S+ATG13: 11; C9orf72L+ATG13: 11). Scale bar = 10 µm; see also Fig EV2. I, J, K. 35S-radiolabeled recombinant FIP200-6xHis segments (I) were added to GST, GST-C9orf72S and GST-C9orf72L immobilized on glutathione-coated beads. 35S-radiolabelled recombinant proteins were visualized by phosphoimager (top panels). Coomassie-stained GST, GST-C9orf72S and GST-C9orf72L in the pull-down samples are shown (bottom panels). The identity of the Coomassie protein bands was confirmed by mass spectrometry (# = E. coli DnaK Chaperonin; * = E. coli 60kD Chaperonin; Appendix Fig S2). I, J, K. 35S-radiolabeled recombinant Myc-ATG13 (J) were added to GST, GST-C9orf72S and GST-C9orf72L immobilized on glutathione-coated beads. 35S-radiolabelled recombinant proteins were visualized by phosphoimager (top panels). Coomassie-stained GST, GST-C9orf72S and GST-C9orf72L in the pull-down samples are shown (bottom panels). The identity of the Coomassie protein bands was confirmed by mass spectrometry (# = E. coli DnaK Chaperonin; * = E. coli 60kD Chaperonin; Appendix Fig S2). I, J, K. 35S-radiolabeled recombinant HA-ULK1 (K) were added to GST, GST-C9orf72S and GST-C9orf72L immobilized on glutathione-coated beads. 35S-radiolabelled recombinant proteins were visualized by phosphoimager (top panels). Coomassie-stained GST, GST-C9orf72S and GST-C9orf72L in the pull-down samples are shown (bottom panels). The identity of the Coomassie protein bands was confirmed by mass spectrometry (# = E. coli DnaK Chaperonin; * = E. coli 60kD Chaperonin; Appendix Fig S2). A, B, C. Cell lysates of HEK293 cells co-transfected with FLAG-FIP200 (A), or HA-ULK1 (B) and either empty vector control, Myc-C9orf72S or Myc-C9orf72L or with Myc-ATG13 (C) and either empty vector control, FLAG-C9orf72S or FLAG-C9orf72L were subjected to immunoprecipitation with anti-Myc (A and B) or anti-FLAG (C) antibodies. Immune pellets were probed for Myc-C9orf72 (A and B), FLAG-C9orf72 (C), FLAG-FIP200 (A), HA-ULK1 (B), or Myc-ATG13 (C) on immunoblots.