The enzyme from the archaeon?Archaeoglobus fulgidus?modifies the wobble base of the CAU anticodon of the archaeal tRNAIle2?at the oxo group in position 2 of cytidine34. This modification is crucial for accurate decoding of the genetic code. In bacteria EC?6.3.4.19, tRNAIle-lysidine synthase, catalyses the modification of [tRNAIle2]-cytidine34?to [tRNAIle2]-lysidine34.