In vivo control of gluconeogenesis in wild-type Neurospora crassa and in the adenylate cyclase-deficient cr-1 (crisp) mutant.

The rate of cycloheximide-resistant incorporation of carbon from 14C]alanine and 14C]acetate into polysaccharidic material was used to study gluconeogenic activity in wild-type Neurospora crassa and in the adenylate cyclase-deficient cr-1 (crisp-1) mutant. The wild-type efficiently utilized alanine and acetate as gluconeogenic substrates, whereas the mutant used acetate efficiently but was unable to use alanine. Cycloheximide-resistant 14C-incorporating activity was sensitive to carbon catabolite effects (repression and inactivation) in the two strains, which suggested that cyclic AMP metabolism was not involved in these regulatory responses. In the wild type, gluconeogenesis was induced by incubation of the cells in the absence of a carbon source. In contrast, cr-1 required supplementation with acetate. This finding suggested that induction of gluconeogenesis in N. crassa could be mediated by metabolites formed in carbon-starved cells. The cr-1 mutant seemed to be deficient in this process and to depend on an exogenous effector to induce gluconeogenesis. Incubation of cr-1 with cyclic AMP partially overcame the acetate requirement for induction of gluconeogenesis.