Synthesis and degradation of proteins and DNA in Streptomyces aureofaciens

The rate of protein synthesis in Streptomyces aureofaciens, measured by incorporation of U-14C-L-leucine into cells, fluctuated during the production phase in the range of 10-15% of the values determined in the phase of intensive growth. Tetracycline partially inhibited the protein synthesis during the growth phase only. The proteins synthesized between the 6th and 18th hour of growth, were 75% degraded by the 48th hour. The DNA synthesis, measured by means of incorporation of 2-14C-thymine into the mycelium, occurred predominantly during the first 24 h of cultivation. Similarly, DNA synthesized between the 6th and 12th hour of cultivation was degraded by 75% after 48 h. The turnover of culture proteins is thus caused largely by degradation of old cells and growth of new ones which are more resistant to tetracycline. The activity of alanine aminotransferase and aspartate aminotransferase increase substantially towards the end of fermentation.