Correlation between rates of degradation of bacterial proteins in vivo and their sensitivity to proteases.

Experiments were undertaken to test whether the relative rates of degradation of proteins in vivo might correlate with their sensitivity to proteases. Various experimental conditions that promote degradation of proteins in Escherichia coli increased sensitivity of average cell proteins to trypsin or other endoproteases, including incorporation of several aminoacid analogs into the proteins, incorporation of puromycin into the polypeptide chain, or frequent errors in translation. Those abnormal proteins that were degraded most rapidly within the cell appear responsible for the increased protease sensitivity of the cell extract. Normal E. coli proteins that rapidly turn over in growing cells are, on the average, more sensitive to trypsin or Pronase than cell proteins that turn over more slowly. The inherent sensitivity of a protein to proteolytic digestion is thus a major determinant of protein half-lives in vivo.