Genetic and biochemical studies of the hexose monophosphate shunt in Neurospora crassa. I. The influence of genetic defects in the pathway on colonial morphology

Abstract

These investigations provide evidence that the N. crassa colonial mutants col-2 and col-3 are defective for two of the HMP shunt enzymes, G6PD and 6PGD respectively. Nutritional studies indicate that both mutants will revert to a more nearly wild-type morphology when they are grown on carbon sources capable of generating NADPH by alternative metabolic pathways. The HMP dehydrogenases are repressed when the organism is grown on acetate or low levels of glutamate. It appears that the lowered steady-state level of NADPH in the colonial mutants is the limiting factor in growth. The principal function of the shunt, apparently, is to supply the reduced NADP required by the cell for its major biosynthetic pathways. The genes coding for the two apparently coordinately controlled dehydrogenases are linked and may be part of a functional region regulating the HMP shunt.