Selective, Energy-dependent Proteolysis in Escherichia coli

Degradation of abnormal proteins, misdirected proteins, proteins missing appropriate partners, and certain naturally unstable proteins is important both for housekeeping and for regulation in all cells. Distinguishing between those proteins that should be degraded and those that should not be degraded necessarily requires recognition of specific signals or motifs. At the same time, because most abnormal proteins are susceptible to degradation whereas the wild-type forms of these same proteins are not, the signals for degradation must be quite general, yet these signals are not present or easily accessible in the wild-type protein. The best hypothesis for the way in which this problem is solved for both prokaryotes and eukaryotes is that the protein features exposed in abnormal proteins but not normally accessible in folded proteins serve as recognition motifs for proteolysis. Very likely, the subset of normal proteins with intrinsically short half-lives also contain recognition motifs that may not be...