RCC1L (RCC1 like) is a mitochondrial inner membrane protein essential for mitochondrial ribosome biogenesis and nucleoid maintenance. The gene encodes three splicing isoforms (RCC1LV1, RCC1LV2, RCC1LV3) that function as guanyl-nucleotide exchange factors coordinating with GTPases (GTPBP10, ERAL1, C4orf14) to facilitate assembly of mitochondrial ribosomal subunits 1. RCC1LV1 associates with the large subunit while RCC1LV3 associates with the small subunit, with both required for proper mitoribosome biogenesis and translation 1. Beyond translation, RCC1L maintains mitochondrial nucleoids and mtDNA stability through mechanisms independent of its translational regulatory function 2. RCC1L interacts directly with NME6 to support oxidative phosphorylation and nucleotide provision for mitochondrial gene expression 3. Disease relevance is substantial: selective RCC1L ablation in dopaminergic neurons causes progressive neurodegeneration with Parkinsonian motor symptoms, including resting tremor, rigidity, and nigrostriatal tract loss, establishing a link between RCC1L dysfunction and Parkinson's disease pathology 4. Additionally, RCC1L variants were identified as genetically associated with systemic lupus erythematosus in genome-wide association studies 5. These findings establish RCC1L as a multifunctional mitochondrial protein critical for both cellular energy metabolism and disease pathogenesis.