Mutants of Escherichia coli with a Defect in the Degradation of Nonsense Fragments

Abstract

Escherichia coli possesses a protein degradation system which can distinguish between normal and aberrant polypeptides^1–8. For example, whereas the enzyme β-galactosidase, coded by the z gene of the lac operon, is itself stable, all the polypeptides produced by nonsense mutations in its structural gene are rapidly degraded in vivo^{1, 3}. This degradation system for abnormal proteins is as sensitive to inhibition of the cell's energy metabolism by substances such as cyanide as is protein synthesis (ref. 4; and B. Shineberg, unpublished observations). Clearly, it is of considerable interest to characterize this system, which we refer to as the Deg system; the genetic locus or loci for this system is denoted by deg.