Introduction: Human ether-à-go-go related gene (hERG, Kv11.1) channel underlies cardiac rapidly activating delayed rectifier K+ current (IKr); hERG mutations contribute to Long QT Syndrome (LQTS). Additionally, reduced repolarization reserve can arise from not only ion channel mutations, but also mutations in ion channel interacting proteins. RING Finger Protein 207 (RNF207) has been identified as a potential modifier for Kv11.1 function, cardiac excitation, and QT interval. Recent studies suggested a link between hERG and RNF207 mutations in LQTS onset and severity, specifically T613M hERG (hERGT613M) and RNF207 frameshift mutation (RNF207G603fs). However, exact molecular mechanisms remain unknown. We hypothesize that RNF207G603fs fails to degrade hERGT613M, allowing a higher population of membrane-bound hERGT613M mutant subunits, thus decreasing functional IKr. Methods and Results: We confirmed ubiquitinylation activity in wild-type RNF207 (RNF207WT). Confocal and super-resolution microscopy in murine and rabbit ventricular cardiomyocytes confirmed co-localization of hERG with RNF207. Functional analyses revealed that the trafficking-defective hERGT613M failed to produce currents. Wild-type hERG (hERGWT) subunits only partially rescued hERGT613M with reduced IKr and faster activation and inactivation kinetics. RNF207WT co-expression with hERGWT and hERGT613M restored IKr, whereas RNF207G603fs failed to rescue IKr. Co-immunoprecipitation of hERGWT pulled down RNF207WT, but not RNF207G603fs. Further analysis using cytoplasmic N- and C-terminal hERGWT deletions (hERGWT-ΔN, hERGWT-ΔC) revealed that RNF207WT pulled down hERGWT-ΔN, but not hERGWT-ΔC. Additionally, time-dependent degradation assays demonstrated increased hERGT613M degradation by RNF207WT, but not RNF207G603fs, via proteasomal degradation. We further tested changes to RNF207 structure using Rosetta molecular modeling software. Conclusion: RNF207WT functions as an E3 ubiquitin ligase for hERG channels. RNF207G603fs, however, failed to degrade hERGT613M and rescue IKr density, suggesting that direct protein-protein interaction is necessary for observed rescue of current. Our data suggest that normal RNF207 function is critical for hERG quality control and, consequently, cardiac repolarization.