Microprotein involved in mitochondrial respiratory chain complex III (ubiquinol-cytochrome c oxidoreductase) and complex IV (mitochondrial cytochrome c oxidase complex) assembly (PubMed:35450818). Required for the formation of mitochondrial supercomplexes (SCs) (PubMed:35450818). Also required for the activation of the NLRP3 inflammasome (By similarity). . This is the function of STMP1 (short transmembrane mitochondrial protein 1, Ensembl gene identifier ENSG00000243317).