Plays an essential role for mitochondrial structure and function, as well as thermogenesis of brown adipocytes. In brown adipose tissue also localizes in the nucleus where it interacts with the chromatin remodeler SMARCA4 to regulate thermogenic genes expression, such as UCP1 (By similarity). May regulate phagocytosis and inflammatory responses to lipopolysaccharide in macrophages (PubMed:31980577). Involved in tumorigenesis and may function as a negative regulator of the p53/TP53 (PubMed:12879013). . This is the function of LETMD1 (LETM1 domain containing 1, Ensembl gene identifier ENSG00000050426).