<scp>RNF219 RING</scp> Finger Domain Mutants Drive Phase Separation to Encapsulate <scp>CCR4</scp> ‐ <scp>NOT</scp> and Promote Cell Proliferation

RING finger protein 219 (RNF219) is a co-factor for the CCR4-NOT deadenylase complex in mammals. Here, we found that mutations within the C3HC4 scaffold of the RING finger domain in RNF219 are capable of forming condensates via liquid-liquid phase separation (LLPS), though the wild-type RING finger domain intrinsically suppresses LLPS. We further demonstrated that the adjacent coiled-coil 1 (CC1) domain promotes the potential of RNF219 to form condensates. Moreover, the mutant RNF219 condensates are able to encapsulate the CCR4-NOT complex, inhibiting the RNA deadenylation activity of CCR4-NOT. Additionally, we observed that RNF219 mutations could promote cell proliferation. These findings suggest a pathogenic mechanism whereby RNF219 mutations could induce CCR4-NOT condensate formation, inhibit deadenylation-dependent mRNA decay and drive cell proliferation.