Domain III of mitochondrial EF-TU (mtEF-TU). mtEF-TU is highly conserved and is 55-60% identical to bacterial EF-TU. The overall structure is similar to that observed in the Escherichia coli and Thermus aquaticus EF-TU. However, compared with that observed in prokaryotic EF-TU the nucleotide-binding domain (domain I) of EF-TUmt is in a different orientation relative to the rest of the structure. Furthermore, domain III is followed by a short 11-amino acid extension that forms one helical turn. This extension seems to be specific to the mitochondrial factors and has not been observed in any of the prokaryotic factors.