Required for O-acetylhomoserine sulfhydrylase (OAHS)-independent homocysteine (Hcy) biosynthesis. Together with MJ0100, catalyzes the condensation of sulfide with aspartate semialdehyde to generate homocysteine. May be involved in the reduction of the disulfide formed in MJ0100. Binds 2 [4Fe-4S] cluster. Amino-acid biosynthesis. May form a complex with MJ0100.