HIF1α carrying long ubiquitin-chains becomes promiscuous in its interaction with ubiquitin-receptors. (A) FAF1 interacts, albeit inefficiently, with HIF1α carrying long ubiquitin-chains (top panel). Flag-UBXN7 or Flag-FAF1 was immunoprecipitated from HeLa cells treated with 10 μM MG132, 1 μM MLN4924, or a combination of the two for two hours. (B) Flag-UBXN7 (green) localizes to the nucleus of HeLa cells. The DNA was stained with DAPI (blue). The scale bar represents 15 μm. (C) RAD23B interacts with slower-migrating, poly-ubiquitylated HIF1α (top panel). Flag-UBXN7 or Flag-RAD23B was immunoprecipitated from HeLa cells using anti-Flag beads. The indicated proteins were detected by western blotting using specific antibodies.