2'-O-METHYL-5-FORMYLCYTIDINE (F(5)CM), A NEW MODIFIED NUCLEOTIDE AT THE WOBBLE POSITION OF 2 CYTOPLASMIC TRNAS(LEU)(NAA) FROM BOVINE LIVER

The nucleotide analysis of a cytoplasmic tRNA(Leu) isolated from bovin e liver revealed the presence of an unknown modified nucleotide N. The corresponding N nucleoside was isolated by different enzymatic and ch romatographic protocols from a partially purified preparation of this tRNA(Leu). Its chemical characterization was determined from its chrom atographic properties, UV-absorption spectroscopy and mass spectrometr ic measurements, as well as from those of the borohydride reduced N nu cleoside and its etheno-trimethylsilyl derivative. The structure of N was established as 2'-O-methyl-5-formylcytidine (f(5)Cm), and its redu ced derivative as 2'-O-methyl-5-hydroxy-methylcytidine (om(5)Cm). By s equencing the bovine liver tRNA(Leu) the structure of the anticodon wa s determined as f(5)CmAA. In addition, the nucleotide sequence showed two primary structures differing only by the nucleotide 47c which is e ither uridine or adenosine. The two slightly differing bovine liver tR NAs-(Leu)(f(5)CmAA) are the only tRNAs so far sequenced which contain f(5)Cm. The role of such a modified cytidine at the first position of the anticodon is discussed in terms of decoding properties for the UUG and UUA leucine codons. Recently, precise evidence was obtained for t he presence of f(5)Cm at the same position in tRNAs(Leu)(NAA) isolated from rabbit and lamb liver. Therefore, the 2'-O-methyl-5-formyl modif ication of cytidine at position 34 could be a general feature of cytop lasmic tRNAs(Leu)(NAA) in mammals.