Mutants of @entity14940 resistant to @entity8776 toxicity are simultaneously derepressed in the presence of @entity3104 for apparently all @entity3104 -repressible activities. Enzyme assays directly demonstrate derepression of @entity1507 , @entity3542 , and @entity8696 reductases, @entity3624 dehydrogenase, urate oxidase, and allantoinase, whereas in vivo tests show that @entity3104 and @entity8776 repression or inhibition (or both) is relieved in these mutants in pathways of @entity1507 assimilation, @entity10043 transport and degradation, and @entity535 , @entity6115 , and @entity6346 catabolism. @entity3104 and @entity8776 uptake is apparently not defective in these mutants, for they grow normally on limiting levels of these ions as sole @entity1568 source. There is no evidence that more than one gene can mutate to produce the @entity8776 resistance (mea(R)) phenotype. Such mutations are semidominant in both heterocaryons and diploids. The ability of mea(R) mutations to effect derepression of activities specified by genes within another nucleus in a heterocaryon shows that the action of the mea product is not restricted to the nucleus. Three types of hypotheses might explain this generalized derepression. First, @entity3104 and @entity8776 might not themselves be co-repressors but might require a metabolic conversion, blocked in these mutants, to become co-repressors. Secondly, the mea locus might specify an activity expressed in mea(R) but not wild-type (mea(S)) strains, which diminishes the concentration of @entity3104 and @entity8776 participating in co-repression. Finally, @entity3104 repression might involve a macromolecular control element specified by the mea(R) locus and common to many or all @entity3104 -repressible systems. The existence of "regulation reversal mutations" at the mea(R) locus and the lack of uniformity and coordination with which different enzymatic activities respond to mutational derepression is most compatible with the last type of hypothesis.

@entity8776 resistance in XXXX .

@entity1568 :: ('MESH:D009584', 'Chemical') :: ['nitrogen'] @entity10043 :: ('MESH:C030985', 'Chemical') :: ['purine'] @entity3624 :: ('MESH:D019820', 'Chemical') :: ['xanthine'] @entity535 :: ('CHEBI:33704', 'Chemical') :: ['amino acid'] @entity3542 :: ('CHEBI:16301', 'Chemical') :: ['nitrite'] @entity6346 :: ('CHEBI:32988', 'Chemical') :: ['amide'] @entity14940 :: ('162425', 'Species') :: ['Aspergillus nidulans'] @entity1507 :: ('CHEBI:48107', 'Chemical') :: ['nitrate'] @entity8696 :: ('MESH:D019811', 'Chemical') :: ['hydroxylamine'] @entity6115 :: ('CHEBI:32952', 'Chemical') :: ['amine'] @entity3104 :: ('MESH:D000644', 'Chemical') :: ['Ammonium', 'ammonium'] @entity8776 :: ('MESH:C027451', 'Chemical') :: ['methylammonium']
@entity14940 :: (162425,Species) :: ['Aspergillus nidulans']
