Promotes mitochondrial protein synthesis. May act as a fidelity factor of the translation reaction, by catalyzing a one-codon backward translocation of tRNAs on improperly translocated ribosomes. Binds to mitochondrial ribosomes in a GTP-dependent manner. . This is the function of Ensembl gene identifier ENSG00000151806 (GUF1, GTP binding elongation factor GUF1).