Regulation of the synthesis of hydrogenase (formate hydrogen-lyase linked) of E. coli

Abstract

The regulation of synthesis of the hydrogenase which is a component of the formate hydrogen-lyase complex was studied by means of a strain of Escherichia coli possessing a transcriptional fusion of the hydrogenase gene (hyd) with the lacZ gene (hyd::lac fusion). Formation of active hydrogenase in the wild strain requires the presence of nickel in the medium; transcription of the hyd gene, however, is independent from the presence of Ni2+. Ni2+ addition to Ni2+-prestarved cells did not lead to any activation of presumptive hydrogenase apoprotein. Regulatory mutants were isolated in which nitrate repression of hyd::lac expression was relieved. Two main classes of regulatory mutants were identified: (i) Mutants with a defect in nitrate reductase; (ii) mutants with a cis-dominant regulatory mutation closely linked to the hyd::lac fusion. In the presence of formate which acts as an inducer, the hyd::lac fusion was also expressed under aerobic conditions. The results infer that nitrate repression of transcription of the hydrogenase structural gene is not effected by nitrate itself but requires the function of the electron transport chain leading to nitrate and that mutations in the promoter/operator region of the hyd cistron may confer insensitivity to redox control both by oxygen and nitrate.

Genetic regulation of formate hydrogenlyase of Escherichia coli: role of the fhlA gene product as a transcriptional activator for a new regulatory gene, fhlB

“…8) (4,25,26,(42)(43)(44)(45). At least two genes coding for the components of the complex have been identified (24,25).…”

“…(J. W. Wendt and K. T. Shanmugam, unpublished observations). So far, only the genes'involved in dihydrogen evolution have been found to require formate for transcription (2,44). The possibility that the FhlB protein is involved in cofactor (Ni) biosynthesis and processing could be discoun'ted because of y the need for formate for transcription.…”

“…Various components of the FHL complex, a unique formate dehydrogenase isoenzyme (FDH-H) and a specific hydrogenase isoenzyme (HYD3), have been identified, and the genes coding for these proteins (fdhF and hyd-17, respectively) have been described (10,24,32,41,45). These genes are transcribed only under anaerobic conditions and require formate as an inducer (4,25,26,42,44). Several other genes whose products are essential for production of one or both of the enzyme activities have also been described.…”

Mutations in trans that affect formate dehydrogenase (fdhF) gene expression in Salmonella typhimurium

“…Strains were tested for H2S production from sulfite by using nutrient agar that contained FeCl2 (1 mM), glucose (10 mM), and Na2SO3 (12 mM) (11). Strains were tested for nitrite reductase activity by scoring for anaerobic growth on Gutnick medium (13) b The mutation in EB137, formerly fhl-IOJ::Mu dl lac (Apr), has been redesignatedfdhFIOJ::Mu dl lac (Apr) (37). ' The mutation in EB138 [hyd-I0J::Mu dl lac (Apr)] pleiotropically affects all three hydrogenases (17).…”

“…Induction of fdhF synthesis requires the presence of formate and molybdate and the absence of electron acceptors like oxygen and nitrate (5,9,31,36,37). There is also a need for an acidic pH in the extracellular environment (23).…”