Catalyzes the formation of the thioether bond required for production of the sporulation killing factor (SKF) from SkfA (PubMed:12817086). Forms the cysteine-methionine thioether bond found in SKF; the acceptor amino acid can be hydrophobic, aromatic or a small hydrophilic amino acid but not a larger hydrophilic amino acid, i.e. Met=Ala, Phe, Leu, Tyr>Asn, Ser>>Gln, Glu, Lys (PubMed:23282011). The relative position of Cys and Met in the substrate cannot be inverted, in vitro the thioether bond cannot be made in the absence of the SkfA propeptide, suggesting this is the first reaction in SKF maturation (PubMed:23282011). In vitro, in the absence of a second substrate, cleaves S-adenosyl-L-methionine into Met and 5'-dA (PubMed:23282011). Binds 2 [4Fe-4S] clusters. One cluster is coordinated with 3 cysteines and an exchangeable S-adenosyl-L-methionine (PubMed:23282011). The other is coordinated via 3 cysteines and maybe direct contact with the SkfA precursor (Probable). By Spo0A (PubMed:12817086) and PhoP, during nutrient starvation, especially phosphate starvation. Repressed by AbrB during normal growth when nutrients are plentiful, in association with the transcriptional repressor Abh. When the skfA-skfB-skfC-skfE-skfF-skfG-skfH operon is deleted, increased rate of spore formation; a double operon deletion (sdpA-sdpC plus skfA-skfH) makes spores even faster (PubMed:12817086). Accelerated cannibalism by skf- cells is seen on solid media but not in liquid media. Belongs to the radical SAM superfamily.