Biotin synthase (BioB), EC:126.96.36.199, catalyzes the last step of the biotin biosynthetic pathway. The reaction consists in the introduction of a sulphur atom into dethiobiotin. BioB functions as a homodimer. Thiamin synthesis if a complex process involving at least six gene products (ThiFSGH, ThiI and ThiJ). Two of the proteins required for the biosynthesis of the thiazole moiety of thiamine (vitamin B(1)) are ThiG and ThiH (this family) and form a heterodimer. Both of these reactions are thought of involve the binding of co-factors, and both function as dimers. This domain therefore may be involved in co-factor binding or dimerization (Finn, RD personal observation).