Studies on protein and nucleic acid turnover in growing cultures of yeast

A study of the utilization of individually 14C-labeled aminoc acid and nucleotide pools in exponentially growing yeast indicated that precursors are converted essentially irreversibly into proteins and nucleic acids. The maximal breakdown rates for each were 0.01 h −1. Employing a more sensitive method, involving an internal nucleic acid purine trap for protein degradation products, the protein breakdown rate was estimated at 2.8· 10 −4 h −1. The proteins therefore have an average half-life of 18 days or longer in cells dividing every 90 minutes. The data indicate that protein breakdown in growing cells is only 4% of that in resting cells. The significance of the difference in protein and possibly nucleic acid stabilities of growing and resting cells is discussed.