As inferred from bovine mitochondrial homologs, MTIF3 (IF-3Mt, IF3mt) binds the 28S ribosomal subunit in preparation for binding mRNA and initiating translation. MTIF3 also dissociates 55S particles that have not already been dissociated by GFM2 plus MRRF and displaces N-formylmethionyl-tRNA from the 28S subunit in the absence of mRNA but cannot displace mRNA from the 28S subunit. The activity of MTIF3 is necessary for translation initiation.. The 28S subunit associates with the matrix-side face of the inner mitochondrial membrane and translation products are inserted directly into the membrane.