REGULATION OF FOLATE-DEPENDENT ENZYME LEVELS IN ASPERGILLUS-NIDULANS - STUDIES WITH REGULATORY MUTANTS

The synthesis of folate-dependent enzymes in Aspergillus nidulans appe ars to be regulated by intracellular pools of homocysteine and methion ine. The results are consistent with the view that homocysteine acts a s an inducer and methionine as a corepressor, but the molecular mechan ism of this regulation is still unknown. Methionine-requiring: mutants , metH2 and metD10, apparently allelic, show deregulation of folate-de pendent enzymes. Most characteristic of the mutants is a repressed lev el of folylpolyglutamate synthetase. New mutations suppressing the met H2 lesion which render folate enzymes insensitive to methionine-mediat ed repression have been isolated. These mutations are likely to identi fy new regulatory genes in folate metabolism.