STRUCTURAL CHARACTERIZATION OF U-ASTERISK-1915 IN DOMAIN-IV FROM ESCHERICHIA-COLI 23S RIBOSOMAL-RNA AS 3-METHYLPSEUDOURIDINE

Mass spectrometry-based methods have been used to study post-transcrip tional modification in the 1900-1974 nt segment of domain IV in 23S rR NA of Escherichia coli, a region which interacts with domain V in form ing the three-dimensional structure of the peptidyl transferase center within the ribosome. A nucleoside constituent of M(r) 258 (U) which occurs at position 1915, within the highly modified oligonucleotide se quence 1911-Psi AACUA Psi-1917, was characterized as 3-methylpseudour idine (m(3) Psi). The assignment was confirmed by chemical synthesis o f m(3) Psi and comparison with the natural nucleoside by liquid chroma tography-mass spectrometry. 3-Methylpseudouridine is previously unknow n in nature and is the only known derivative of the common modified nu cleoside pseudouridine thus far found in bacterial rRNA.