Intracellular protein degradation in Neurospora crassa.

In exponentially growing cultures of Neurospora crassa, the basal rate of protein degradation increases as the constant of the rate of growth decreases, so that in slow growing cells (mu = 0.13) the rate of protein degradation is about 25% of the rate of protein accumulation. During glucose starvation and shift-down transition of growth, the rate of protein degradation is greatly enhanced, and a moderate reduction (about 30%) of the ATP level is observed. Treatment of glucose-starved cells with 2-deoxyglucose reduces the ATP content by 70% and blocks protein degradation. The addition of cycloheximide, given at the onset of glucose starvation, prevents the enhancement of protein degradation; instead cycloheximide is without effect if added when proteolysis has already started. At a supraoptimal temperature (42 degrees C) the basal rate of protein degradation is not stimulated, contrary to the behavior observed in bacteria. Guanosine nucleotides, which appear to have a regulatory role for protein degradation in bacteria, are not found in N. crassa.