tRNA (cytidine³⁴-2'-O)-methyltransferase (EC 2.1.1.207, yibK (gene), methyltransferase yibK, TrmL, tRNA methyltransferase L, tRNA (cytidine^34/5-carboxymethylaminomethyluridine³⁴-2'-O)-methyltransferase) is an enzyme with systematic name S-adenosyl-L-methionine:tRNA (cytidine^34/5-carboxymethylaminomethyluridine³⁴-2'-O)-methyltransferase.^[1] This enzyme catalyses the following chemical reaction

(1) S-adenosyl-L-methionine + cytidine³⁴ in tRNA ${\displaystyle \rightleftharpoons }$ S-adenosyl-L-homocysteine + 2'-O-methylcytidine³⁴ in tRNA

(2) S-adenosyl-L-methionine + 5-carboxymethylaminomethyluridine³⁴ in tRNALeu ${\displaystyle \rightleftharpoons }$ S-adenosyl-L-homocysteine + 5-carboxymethylaminomethyl-2'-O-methyluridine³⁴ in tRNALeu

The enzyme from Escherichia coli catalyses the 2'-O-methylation of cytidine or 5-carboxymethylaminomethyluridine at the wobble position at nucleotide 34 in tRNALeuCmAA and tRNALeucmnm5UmAA.