Elongation factor Ts, mitochondrial is a protein that in humans is encoded by the TSFM gene. It is an EF-Ts homolog. This gene encodes a mitochondrial translation elongation factor. The encoded protein is an enzyme that catalyzes the exchange of guanine nucleotides on the translation elongation factor Tu during the elongation step of mitchondrial protein translation. Mutations in this gene are associated with combined oxidative phosphorylation deficiency-3 syndrome. Alternate splicing results in multiple transcript variants.