AT LEAST 4 REGULATORY GENES CONTROL SULFUR METABOLITE REPRESSION IN ASPERGILLUS-NIDULANS

Mutations in four genes: sconA (formerly suA25meth, mapA25), sconB (fo rmerly mapB1), sconC and sconD, the last two identified in this work, relieve a group of sulphur amino acid biosynthetic enzymes from methio nine-mediated sulphur metabolite repression. Exogenous methionine has no effect on sulphate assimilation in the mutant strains, whereas in t he wild type it causes almost complete elimination of sulphate incorpo ration. In both mutant and wild-type strains methionine is efficiently taken up and metabolized to S-adenosylmethionine, homocysteine and ot her compounds. scon mutants also show elevated levels of folate-metabo lizing enzymes which results from the large pool of homocysteine found in these strains. The folate enzymes apear to be inducible by homocys teine and repressible by methionine (or S-adenosylmethionine).