A Modified Uridine in the Anticodon of E. Coli

The anticodon of an ochre-suppressing derivative of E. coli tRNA^Tyr_L, previously identified as UUA, can contain a modified uridlne (U⁺) in the first position. The novel modified nudeotide has been identified by twodimensional thin layer chromatography following RNase T₂ digestion of anticodon contalnlng fragments. U⁺_R is found in less than stolchiometric molar yields in preparations of tRNA^Tyr_L Su⁺_Oc. The electrophoretlc mobility of U⁺_P is the same as Up at pH 3.5 and PH 7.5. U⁺ probably does not contain sulfur since it cannot be labeled with ³⁵S in vivo incorporation experiments.