Chemical conversion of cytidine residues into 4-thiouridines in yeast tRNAPhe. 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.