Catalyzes two activities which are involved in the biotine biosynthesis: the conversion of dethiobiotin (DTB) to biotin by the insertion of a sulfur atom into dethiobiotin via a radical-based mechanism, and the transfer of the alpha-amino group from S-adenosyl-L-methionine (SAM) to 7-keto-8-aminopelargonic acid (KAPA) to form 7,8-diaminopelargonic acid (DAPA). (4R,5S)-dethiobiotin + [sulfur carrier]-SH + 2 reduced [2Fe-2S]-[ferredoxin] + 2 S-adenosyl-L-methionine = 2 5'-deoxyadenosine + [sulfur carrier]-H + biotin + 2 L-methionine + 2 oxidized [2Fe-2S]-[ferredoxin] (8S)-8-amino-7-oxononanoate + S-adenosyl-L-methionine = (7R,8S)-7,8-diammoniononanoate + S-adenosyl-4-methylsulfanyl-2-oxobutanoate Binds 1 [4Fe-4S] cluster. The cluster is coordinated with 3 cysteines and an exchangeable S-adenosyl-L-methionine. Binds 1 [2Fe-2S] cluster. The cluster is coordinated with 3 cysteines and 1 arginine. Cofactor biosynthesis; biotin biosynthesis; biotin from 7,8-diaminononanoate: step 2/2. Cofactor biosynthesis; biotin biosynthesis; 7,8-diaminononanoate from 8-amino-7-oxononanoate (SAM route): step 1/1. Homodimer. In the N-terminal section; belongs to the radical SAM superfamily. Biotin synthase family. In the C-terminal section; belongs to the class-III pyridoxal-phosphate-dependent aminotransferase family. BioA subfamily. Extended N-terminus.