REGULATION OF SUCCINATE-DEHYDROGENASE (SDHCDAB) OPERON EXPRESSION IN ESCHERICHIA-COLI IN RESPONSE TO CARBON SUPPLY AND ANAEROBIOSIS - ROLE OF ARCA AND FNR

Succinate dehydrogenase (SDH) of Escherichia coil, the sole membrane-b ound enzyme of the tricarboxylic acid cycle, participates in the aerob ic electron-transport pathway to generate energy via oxidative phospho rylation reactions. Previous studies have established that succinate d ehydrogenase (SDH) synthesis is elevated by aerobiosis and supressed d uring growth with glucose. To examine how the sdhCDAB genes that encod e SDH are regulated by changes in the environment, sdh-lacZ fusions we re constructed and analysed in vivo following cell growth under a vari ety of alternative culture conditions, Expression of sdh-lacZ was high est under aerobic conditions and was decreased 10-fold in the absence of oxygen, The fnr and arcA gene products are required for this oxygen control and each acts to repress sdhC-lacZ expression, Expression of sdh-lacZ also varied 10- to 14-fold depending on the type of carbon su bstrate used or the medium richness, This control was shown to be inde pendent of the crp and fruR gene products, and indicates that some oth er regulatory element exists in the cell to adjust SDH enzyme levels a ccordingly, Iron and haem availability affected sdhC-lacZ expression b y two- to three-fold. Lastly, sdhC-lacZ expression was shown to vary w ith the cell growth rate during aerobic and anaerobic conditions,