Mitochondrial tRNA(Trp)s Imply a Eubacterial Origin.

Three mitochondrial tRNA(Trp)s genes from Oryza sativa, Homo sapiens and Saccharomyces serevisea were constructed. In vitro transcripts of these mitochondrial tRNA(Trp)s genes were able to be tryptophanylated by Bacillus subtilis tryptophanyl-tRNA synthetase (TrpRS), but could not be catalyzed by TrpRS from rat liver. Kinetic assay showed that B. subtilis TrpRS had half the binding capacity for mitochondrial tRNA(Trp)s than for wild type tRNA(Trp). While in the catalytic efficiency, the k(cat)/K(m) value of mitochondrial tRNA(Trp)s from O.sativa and S.serevisea by B.subtilis enzyme was reduced by 400-fold and 1 200-fold respectively as that of B.subtilis tRNA(Trp). Experimental results suggested that mitochondrial tRNA(Trp)s implied a eubacterial origin.