ABSTRACT
Divalent metal ions play a crucial role in RNA structure and catalysis. Phosphorothioate substitution and manganese rescue experiments can reveal phosphate oxygens interacting specifically with magnesium ions essential for structure and/or activity. In this study, phosphorothioate interference experiments in combination with structural sensitive circular dichroism spectroscopy have been used to probe molecular interactions underlying an important RNA structural motif. We have studied a synthetic model of the P4-P6 triple-helical domain in the bacteriophage T4 nrdB group I intron, which has a core sequence analogous to the Tetrahymena ribozyme. Rp and Sp sulfur substitutions were introduced into two adjacent nucleotides positioned at the 3' end of helix P6 (U452) and in the joining region J6/7 (U453). The effects of sulfur substitution on triple helix formation in the presence of different ratios of magnesium and manganese were studied by the use of difference circular dichroism spectroscopy. The results show that the pro-Sp oxygen of U452 acts as a ligand for a structurally important magnesium ion, whereas no such effect is seen for the pro-Rp oxygen of U452. The importance of the pro-Rp and pro-Sp oxygens of U453 is less clear, because addition of manganese could not significantly restore the triple-helical interactions within the isolated substituted model systems. The interpretation is that U453 is so sensitive to structural disturbance that any change at this position hinders the proper formation of the triple helix.
Subject(s)
Ions/chemistry , Metals/chemistry , RNA/chemistry , Animals , Base Sequence , Binding Sites , Circular Dichroism , Introns , Ligands , Magnesium/chemistry , Magnesium/pharmacology , Manganese/pharmacology , Molecular Sequence Data , Nucleic Acid Conformation , Oxygen/chemistry , Protein Structure, Tertiary , RNA/metabolism , Sulfur/chemistry , Temperature , Tetrahymena/chemistryABSTRACT
[see reaction]. Silylcupration reaction of 1,3-dienes with a cyanocuprate reagent, PhMe2SiCuCNLi, followed by an electrophilic trapping has been reported for the first time. The use of allylic phosphates as electrophiles resulted in a highly regioselective reaction with overall 1,4-addition of the silyl and allyl moieties across the diene.
ABSTRACT
[formula: see text] Silylcupration of allenes with a lower order silylcuprate reagent followed by an electrophilic trapping reaction with allylic diphenyl phosphates has been studied. This reaction provides a new route to 1,4-diene systems having an allylsilane moiety.
