The methylthiotransferases MiaB ((dimethylallyl)adenosine tRNA MTTase miaB protein) and RimO catalyze sulfur insertion into tRNAs and ribosomal protein S12, respectively. Both belong to a sub-group of Radical-SAM enzymes that bear two [4Fe-4S] clusters. They are the representative members of the methylthiotransferase (MTTases) or miaB-like family. MTTases consist of an N-terminal MTTase domain, a central radical generating fold and a C-terminal TRAM domain. Structural domains comprising this superfamily share the structure of the N-terminal MTTase domain, which domain contains 3 cysteines that bind the two cited [4Fe-4S] clusters, one of them being radical generating and thus, involved in the thiolation reaction PMID:23542644.