Chemical conversion of cytidine residues into 4-thiouridines in yeast tRNA^Phe. Determination of the modified cytidines

Abstract

Treatment of yeast phenylalanine tRNA with pressurized hydrogen sulfide results in conversion of cytidine residues into 4-thiouridine residues. Under conditions leading to an average modification of one cytidine per tRNA molecule 9 positions are thiolated. The 4-thiouridine residues are distributed along the tRNA molecule. Four of the reactive cytidines are located in single-stranded regions: Cm32 , C60 , C74 and C75 . The five others are located in base pairs: C2, C27, C56 , C61 and C63 . Importance of replacement of an amino group by a thiol group on hydrogen bonding and on biological activity of the modified tRNA is discussed.

Mapping the central fold of tRNA2fMet in the P site of the Escherichia coli ribosome

“…This may be due to the fact that 10 of the 13 U residues in tRNA^Mcl are located in non-base-paired regions; only U50, U27, and U24 are base-paired. In the case of U50, which pairs with G64 in the T stem, the substitution of U by s4U should not lead to a distortion of the helix because the geometry of the s4U-G pair is similar to that of the U-G pair (Psoda et al, 1974;Riehl et al, 1984). In contrast, the configuration of the D or anticodon stems could be perturbed by the incorporation of s4U at position 24 or 27, respectively, as the geometry of the s4U24-A11 or s4U 27-A43 pa ir may differ somewhat from the U24-A11 or U27-A43 pair (Saenger & Suck, 1971).…”

Use of Specific Chemical Reagents for Detection of Modified Nucleotides in RNA

“…In both cases, the first nucleophilic attack occurs at the C6, and only then does the C4 position react [ 33 , 39 ]. Using hydrogen sulfide under high pressure, cytidines can be converted into s 4 U as the result of a nucleophilic attack at the carbon 4 position [ 41 , 42 ], which might be preceded by an initial nucleophilic attack at the C6.…”