title: Nuclear magnetic resonance studies on the tertiary folding of transfer ribonucleic acid: assignment of the 7-methylguanosine resonance.
abstract: Analysis of the low-field nuclear magnetic resonance (NMR) spectra of several class 1 D4V5 transfer ribonucleic acid (tRNA) species containing 7-methylguanosine in their variable loops reveals a set of six to seven tertiary base pair resonances, one of which is always located at ca. --13.4 ppm. Other tRNA species which do not contain 7-methyl-guanosine do not contain the tertiary resonance at --13.4 ppm. Chemical removal of 7-methylguanosine from several tRNAs containing the same dihydrouridine (DHU) helix sequence as yeast tRNAPhe results in the loss of the --13.4-ppm tertiary resonance. In the initiator methionine tRNA, which contains a different DHU helix sequence, the 7-methylguanosine hydrogen bond has been assigned at --14.55 ppm by chemical removal of this residue. In these experiments the aromatic C8H proton of 7-methylguanosine was also assigned (--9.1 ppm). The unexpectedly low-field position of the 7-methylguanosine resonance is explained by the deshielding effect of the delocalized positive charge in this nucleoside.
mesh_terms: D001482:Base Composition; D001483:Base Sequence; D004926:Escherichia coli; D005998:Glycine; D006151:Guanosine / Q000031:analogs & derivatives*; D009682:Magnetic Resonance Spectroscopy; D008715:Methionine; D009690:Nucleic Acid Conformation; D010649:Phenylalanine; D012343:RNA, Transfer; D014633:Valine
chemical_list: D006151:Guanosine; C016578:7-methylguanosine; D010649:Phenylalanine; D012343:RNA, Transfer; D008715:Methionine; D014633:Valine; D005998:Glycine