The effect of protein degradation on cellular growth characteristics.

The role of protein degradation in cellular proliferation was investigated by measurements of the rates of degradation of labile and stable proteins for a number of cell types under various growth conditions. The rate of protein degradation was found to be a relatively invariant parameter in that it did not change after strong inhibition of protein synthesis with cychloheximide or histidinol, it was the same in both exponential and stationary phase, and it did not correlate with the presence or absence of malignant transformation. Using three different cell types with widely differing division rates, the rate of cell division and DNA synthesis (in %/hr) was found to be precisely equal to the rate of protein accumulation (in %/hr) , i.e., to the rate of protein synthesis minus the rate of protein degradation. Division rates between the different cell types appeared to be determined chiefly by the rate of protein synthesis though, especially at low division rates, the rate of protein degradation could represent a large component of the protein accumulation rate.