The function of MARCHF5 (membrane associated ring-CH-type finger 5, ENSG00000198060) is as follows. Mitochondrial E3 ubiquitin-protein ligase that plays a crucial role in the control of mitochondrial morphology by acting as a positive regulator of mitochondrial fission and as an important regulator of immune response (PubMed:16874301, PubMed:17606867, PubMed:26246171, PubMed:31881323). Plays a crucial role in maintaining mitochondrial homeostasis by regulating the dynamics of mitochondria through the ubiquitination of key proteins involved in fission and fusion such as FIS1, DNM1L and MFN1 (PubMed:16874301, PubMed:17606867). Acts as a critical determinant of mitotic apoptosis through both MCL1- dependent and -independent pathways (By similarity). Turns off persistent immune signaling by degrading oligomeric complexes of retinoic acid-inducible gene I/DDX58 and mitochondrial antiviral- signaling protein/MAVS formed upon RNA virus infection (PubMed:26246171, PubMed:31881323, PubMed:40071916). Promotes STING- mediated type-I interferon production via 'Lys-63'-linked ubiquitination of STING1 thereby preserving its activity and preventing the formation of inactive STING1 polymers (PubMed:37916870). Plays also an essential role in the formation of PEX3-containing vesicles in the de novo biogenesis of peroxisomes from mitochondria (PubMed:39423820, PubMed:39423819). Acts as a regulator of NLRP3 inflammasome activation on the mitochondria by mediating the 'Lys-27'-linked polyubiquitination of NLRP3, positively regulating the NLRP3-NEK7 complex formation and NLRP3 oligomerization (PubMed:37575012). {ECO:0000250|UniProtKB:Q3KNM2, ECO:0000269|PubMed:16874301, ECO:0000269|PubMed:17606867, ECO:0000269|PubMed:19741096, ECO:0000269|PubMed:20103533, ECO:0000269|PubMed:37575012, ECO:0000269|PubMed:37916870, ECO:0000269|PubMed:39423819, ECO:0000269|PubMed:39423820, ECO:0000269|PubMed:40071916}. (Microbial infection) Plays a positive role in Japanese encephalitis virus infection by catalyzing the 'Lys-27'-linked polyubiquitination of viral E protein to facilitate efficient viral attachment. .