An "elongated" translation elongation factor Tu for truncated tRNAs in nematode mitochondria

We have found the gene for a translation elongation factor Tu (EF-Tu) homol ogue in the genome of the nematode Caenorhabditis elegans, Because the corr esponding protein was detected immunologically in a nematode mitochondrial (mt) extract, it could be regarded as a nematode mt EF-Tu. The protein poss esses an extension of about 57 amino acids (we call this domain 3') at the C terminus, which is not found in any other known EF-Tu, Because most nemat ode mt tRNAs lack a T stem, domain 3' may be related to this feature. The n ematode EF-Tu bound to nematode T stem-lacking tRNA, but bacterial EF-Tu wa s unable to do so. A series of domain exchange experiments strongly suggest ed that domains 3 and 3' are essential for binding to T stem-lacking tRNAs, This finding may constitute a novel example of the co-evolution of a struc turally simplified RNA and the cognate RNA-binding protein, the latter havi ng apparently acquired an additional domain to compensate for the lack of a binding site(s) on the RNA.