Figure 5.

IscS and TusA connect the sulfur transfer pathway for the synthesis of Moco and for tRNA thiolation in E. coli. Formation of the thiocarboxylate group on MoaD (upper part). cPMP is converted to MPT by the transfer of two sulfur groups from the C-terminal thiocarboxylate of the MoaD. Regeneration of the MoaD thiocarboxylate group by MoeB. MoaD receives its sulfur by a persulfide-sulfur relay system consisting of IscS and TusA. Formation of cmnm⁵s²U and mnm⁵s²U in E. coli (lower part). Sulfur relay system from IscS via TusA, 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 or mnm⁵s²U by MnmG, MnmE and MnmC.