Isolation of 5-fluorouracil-containing 5S ribonucleic acid from Escherichia coli

Synthesis and biological applications of fluoro-modified nucleic acids

Owing to the unique physical properties of a fluorine atom, incorporating fluoro-modifications into nucleic acids offers striking biophysical and biochemical features, and thus significantly extends the breadth and depth of biological applications of nucleic acids. In this review, fluoro-modified nucleic acids that have been synthesized through either solid phase synthesis or the enzymatic approach are briefly summarised, followed by a section describing their biomedical applications in nucleic acid-based therapeutics, ¹⁸F PET imaging and mechanistic studies of DNA modifying enzymes. In the last part, the utility of ¹⁹F NMR and MRI for probing the structure, dynamics and molecular interactions of fluorinated nucleic acids is reviewed.

Raman and 19F(1H) nuclear Overhauser evidence for a rigid solution conformation of Escherichia coli 5-fluorouracil 5S ribonucleic acid

Escherichia coli cells grown on a medium containing 5-fluorouracil (FU) produce 5S RNA whose uracil residues are approximately 80% replaced by FU. The Raman spectra of native and FU-5S RNA are very similar, confirming similar solution conformations for the two species and a highly base-stacked structure in solution. The 254-MHz 19F NMR spectrum of FU-5S RNA shows that the 20-odd FU residues reside in at least ten distinct chemical environments, suggesting a highly ordered structure. Comparison of theoretical and experimental 19F(1H) nuclear Overhauser enhancements demonstrates definitively that virtually all the labeled uracils are bound to a rigid macromolecular frame, with a rotational correlation time of about 19 ns or longer. Since these uracils are widely distributed throughout the nucleotide primary sequence, it may be concluded that the entire FU-5S RNA solution structure is relatively rigid, in agreement with the most recently proposed "cloverleaf" secondary structural model for native prokaryotic 5S RNA.