Degradation of Abnormal Proteins in 'Escherichia Coli'. Formation of Protein Inclusions in Cells Exposed to Amino Acid Analogs.

摘要

Cells of Escherichia coli selectively degrade proteins that have incorporated amino acid analogs. Within 1 hour after exposure of cells of canavanine, 50% of the analog-containing proteins were degraded to acid-soluble form. At the same time, no net loss of canavanine-containing protein occurred from the 100,000 x g supernatant. Instead, most of the proteins containing the analog, unlike normal ones, accumulated in particulate fractions sedimenting at 10,000 x g or 100,000 x g. They were then lost from these fractions concomitant with the degradation of the abnormal proteins. The loss of such proteins from particulate fractions accounted for all of the protein degraded to acid-soluble form. Similar observations were obtained after incorporation of other analogs or puromycin. Findings suggest that (a) the presence of amino acid analogs in proteins can make them less soluble, and (b) the inclusions are formed by the spontaneous precipitation of abnormal proteins rather than by an active granule-forming process.