SULFUR AMINO-ACID-METABOLISM IN SCHIZOSACCHAROMYCES-POMBE - OCCURRENCE OF 2 O-ACETYLHOMOSERINE SULFHYDRYLASES AND THE LACK OF THE REVERSE TRANSSULFURATION PATHWAY

The fission yeast Schizosaccharomyces pombe has a unique organization of sulfur amino acid metabolism: it has two distinct O-acetylhomoserin e sulfhydrylases (homocysteine synthases). Similar to Enterobacteriace ae, S. pombe lacks cystathionine beta-synthase and cystathionine gamma -lyase - the enzymes of the reverse transsulfuration pathway, by which methionine is readily metabolized to cysteine - a likely effector in the sulfur metabolite repression system. Consequently no repression of sulfate assimilation is observed when methionine is added to the grow th medium.