FIG. 4.

HPLC profile of pyrimidine region of thionucleosides. (Top) Modified nucleoside HPLC profile of digested tRNA isolated from wild-type (wt) parent strain MC1061, with thionucleosides labeled. (Middle) Same profile from ΔiscS strain CL100. (Bottom) Profile from strain CL100 with plasmid pCL010 (wild-type iscS). The peak near 4-thiouridine in the middle panel is an unidentified compound that was present in all chromatograms but was revealed more clearly in the absence of 4-thiouridine. I independently verified at 330 nm that strain CL100 lacked 4-thiouridine (see Fig. 6) (16). s⁴U, 4-thiouridine; s²C, 2-thiocytidine; mnm⁵s²U, 5-methylaminomethyl-2-thiouridine.