THE CADMIUM-STRESS STIMULON OF ESCHERICHIA-COLI K-12

The influence of cadmium on stress protein production in Escherichia c oli K-12 (strain MG1655) was analysed using two-dimensional polyacryla mide gel electrophoresis and the gene-protein database of E. coli K-12 . Cadmium (273 mu M) caused complete but transient inhibition of growt h accompanied by the synthesis of cadmium-induced proteins (CDPs). It was found that some CDPs induced during the growth-arrested phase belo ng to the heat-shock, oxidation stress, SOS and stringent response reg ulons, while others are general stress inducible proteins (e.g. H-NS, UspA). In addition, trigger factor, adenylate kinase, W-protein, the c old shock protein G041.2, and seven unknown proteins whose synthesis i s not known to be controlled by a global regulator, were identified as immediate responders to cadmium exposure. The rate of synthesis of mo st of the immediate responders to cadmium exposure decreased when the growth of the cells resumed. However, seven CDPs, including those enco ded by argl, tyrA and xthA, maintained a high production rate during g rowth in the presence of cadmium. Two of the unidentified proteins wer e N-terminally sequenced by Edman degradation. The N-terminal amino ac id sequence of one of these proteins (designated F023.3) matches the E . coli open reading frame o216. This ORF is similar to the N-terminal third of the copper-binding protein amine oxidases (encoded by maoA) o f both E. coli and Klebsiella pneumoniae (K. aerogenes). The other N-t erminally sequenced protein (designated C044.6) matches perfectly the product of the metK gene, S-adenosylmethionine synthetase I. In compar ison to untreated cells, cadmium-stressed cells were found to recover more rapidly during subsequent stress conditions, such as ethanol, osm otic, heat shock, and nalidixic acid treatment. The role of the CDPs i s discussed in view of their physiological assignments in the cell.