MIEF1-MP, also called alternative mitochondrial elongation factor 1 (MIEF1) protein (AltMIEF1), or MIEF1 upstream open reading frame protein, is involved in the regulation of mitochondrial fission mediated by dynamin-1-like protein (DNM1L). It positively regulates mitochondrial translation []. MIEF1-MP belongs to the Complex1_LYR-like superfamily that consists of proteins of diverse functions that are exclusively found in eukaryotes and contain the conserved tripeptide 'LYR' close to the N terminus.