The Biosynthesis of the Molybdenum Cofactor in Escherichia coli and Its Connection to FeS Cluster Assembly and the Thiolation of tRNA

Figure 10

Chemical structure of thio-containing tRNA modifications. Shown are the secondary structure and the positions of thiolated nucleosides in tRNA. Abbreviations: s⁴U, 4-thiouridine; s²U, 2-thiocytidine; mnm⁵s²U, 5-methylaminomethyl-2-thiouridine; ms²i⁶A, 2-methylthio-N6-isopentenyladenosine; ms²io⁶A, N6-(4-hydroxyisopentenyl)-2-methylthioadenosine. Each number represents the nucleoside position in the tRNA. On the left-hand side the sulfur transfer pathway for the formation of s²U is shown. The sulfur transfer involves the initial sulfur mobilization by IscS, sulfur transfer to TusA-C19, and further transfer via TusD in the TusBCD complex, TusE to MnmA, which binds and activates the tRNA by adenylation. After formation, s²U is further modified to form cmnm⁵s²U and mnm⁵s²U.