Strong selective pressure to use G:U to mark an RNA acceptor stem for alanine

A study of mitochondria from Caenorhabditis elegans which not only has the G:U pair preserved but also proximal nucleotides that inhibits charging by a nonmitochondrial enzyme is presented. Mitochondrial alanyl-tRNA synthetase from C. elegans has been cloned and its microhelix oligonucleotides have been assessed as substrates for aminoacylation. Results show that G:U recognition continues even with an acceptor helix that does not recognize nonmitochondrial systems. The mitochondrial enzyme is similar to other alanine enzymes including the well-studied Escherichia coli protein.