Siroheme biosynthesis in Saccharomyces cerevisiae requires the products of both the MET1 and MET8 genes.

Siroheme is a uroporphyrinogen III-derivative used by sulfite reductase as a prosthetic group. We investigated in Saccharomyces cerevisiae the possible involvement in siroheme biosynthesis of three genes, MET1, MET8 and MET20. The MET1 gene from S. cerevisiae was cloned and shown to be the same gene as MET20. Sequence similitudes as well as complementation studies indicate that Met1p and Met8p are both involved in siroheme biosynthesis. In addition, we show formally that S. cerevisiae does not need vitamin B12 for growth.