Studies on Tyrosine Transfer Ribonucleic Acid, a Sulfur-rich Species from Escherichia coli

Abstract A purified species of tyrosine transfer RNA has been isolated by countercurrent techniques and shown to contain 2 4-thiouridylate residues per molecule. These thionucleotides may be titrated quantitatively with p-hydroxymercuribenzoate. Denaturation studies with heat or urea indicate that they are probably hydrogen-bonded in the tRNA. Iodine oxidation of the purified tRNA leads to the formation of a disulfide bond between the thionucleotides without, in this case, changing the amino acid acceptor activity of the molecule. Disulfide formation is accompanied by a slight loss in secondary structure, as shown by a decrease in the Tm and an increase in the E(p). Studies in the ultracentrifuge indicate that the sedimentation of the disulfide form is not greatly changed from that of the native form and that therefore the disulfide bond must be intra- rather than intermolecular.