Enzymatic conversion of cytidine to lysidine in anticodon of bacterial tRNAlle -: an alternative way of RNA editing

In most organisms, the AUA triplet codes for isoleucine (Ile), whereas in a few organelles it codes for methionine (Met). In bacteria, this A-ending triplet is decoded by an unusual tRNA harboring a Met anticoclon CAU, where cytidine at the wobble position 34 (C34) is post-transcriptionally modified to a 2-lysyl cytidine (lysidine), abbreviated as (k(2)C). Now, the bacterial gene tilS, which encodes the enzyme catalyzing the lysylation of C34 in the precursor tRNA(Ile)( CAU), thereby leading to the formation of tRNA(Ile)(k 2 CAU), has been identified. The formation of lysidine by this essential enzyme allows recognition of tRNA(Ile) (k(2)CAU) by Ile-tRNA synthetase and switches the base pairing of the tRNA from AUG (Met) to AUA (Ile). This base change is reminiscent of C-to-U type of RNA editing of some mitochondrial tRNAs.