CLONING AND SEQUENCE-ANALYSIS OF THE HUMAN MITOCHONDRIAL TRANSLATIONAL INITIATION-FACTOR-2 CDNA

Complete cDNAs encoding human mitochondrial translational initiation f actor 2 (IF-2(mt)) have been obtained from liver, heart, and fetal bra in cDNA libraries. These cDNAs have a long open reading frame 2181 res idues in length encoding a protein of 727 amino acids. Overall, human IF-2(mt) has 30-40% identity to the corresponding prokaryotic factors. Surprisingly, it is no more homologous to yeast IF-2(mt) than to the IF-2s from bacterial sources. The greatest region of conservation lies in the G-domain of this factor with less conservation in the COOH-ter minal half of the protein and very little homology near the amino term inus. The 5'-untranslated leaders of the liver and heart cDNAs contain a number of short open reading frames. These sequences may play a rol e in the translational activity of the IF-2(mt) mRNA. Northern analysi s indicates that the IF-2(mt) gene is expressed in all tissues but tha t the level of expression varies over a wide range.