SUMMARY: The position of a gene (fnr) that is essential for growth of Escherichia coli with fumarate or nitrate as electron acceptor was located within an 11 -5 kb HindIII fragment of bacterial DNA by deletion analysis with fnr transducing phages (Afnr) and by sub-cloning restriction fragments into multicopy plasmids. The functional gene was isolated in a 1-65 kb BamHI-Hind111 fragment of a hybrid plasmid pGS24. The fnr gene product wasidentified as a protein of M 31 000, by post-infection labelling and by the maxicell method. Organisms containing the multicopy plasmid (pGS24) overproduced fumarate reductase to the same extent as cultures containing a comparable fumarate reductase plasmid (pNU3 1) during anaerobic growth; thefnr plasmid also overcame the repression of fumarate reductase synthesis that is normally observed during aerobic growth. Similar effectson nitrate reductase synthesis were also observed. The results support the view that thefnr gene product functions as a positive regulator or a specific sigma factor for expression of anaerobic energy-generating systems.


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