Lysidine (nucleoside)
Lysidine is an uncommon nucleoside, rarely seen outside of tRNA. It is a derivative of cytidine in which the carbonyl is replaced by the amino acid lysine. The first position, i.e. the wobble base, in the anti-codon of the eubacterial isoleucine-specific tRNA pertaining to the AUA codon is typically changed from a cytidine which would pair with guanosine to a lysidine which will base pair with adenosine. Lysidine improves translation fidelity because uridine cannot be used at this position even though it is a conventional partner for adenosine since it will also "wobble base pair" with guanosine. Lysidine is denoted as L or k2C.