RAC1 and cancer: Notably, the Catalogues of Somatic Mutations in Cancer (COSMIC v96, Sanger Institute) lists Arg332 at the WT HACE1–RAC1 interface as the most reported mis‐sense substitution site linked to cancer in HACE1 (Table S6, Supporting Information).[33] Our in vitro ubiquitination assay showed that mutation at Arg332 in the MID domain increased RAC1 ubiquitination (Figure 3C).