The molecular genetics of superoxide dismutase in E. coli. An approach to understanding the biological role and regulation of SODS in relation to other elements of the defence system against oxygen toxicity.

Superoxide-mediated oxidative stress initiates a chain of events resulting in numerous cellular injuries. We have used genetics and E. coli to investigate the role and regulation of superoxide dismutase (SOD) and its relationship with the other constituents of the oxygen toxicity defence system. Structural SOD genes have been cloned and sequenced, permitting us to refine structural analysis and to isolate SOD-deficient mutants. The conditional oxygen sensitivity of these mutants, together with their increased mutation rate, demonstrated the essential biological role of SOD. Furthermore the complementation of SOD-lacking E. coli deficiencies by introducing a plasmid containing the gene encoding the human SOD supported the proposal that superoxide dismutation is the physiological function of SOD. Regulation of the MnSOD, through which the global SOD level in E. coli is modulated, has been studied using operon and protein fusions with the lactose operon, and led to the conclusion of a multicontrol of MnSOD. Isolation and characterization of regulation mutants are in progress, with the aim of identifying effectors and targets involved in the response to superoxide-mediated oxidative stress.