STABILITY OF ESCHERICHIA-COLI SODA MESSENGER-RNA AND IDENTIFICATION OF THE TRANSCRIPTIONAL START SITE(S) UNDER DIFFERENT ENVIRONMENTAL AND OXIDATIVE STRESSES

Manganese-containing superoxide dismutase (MnSOD-sodA) in Escherichia coli (E. coli) is regulated at the transcriptional level as observed i n studies using both operon and gene fusions. In this paper we examine the regulation of sodA gene at the level of mRNA. We examine the effe cts of several aerobic inducing conditions (i.e., nalidixic acid, para quat, or 2,2'-dipyridyl) on mRNA stability, transcription initiation, and translation. The half-life of sodA mRNA was found to be approximat ely 3-4 min, showing no differences in mRNA stability between induced and uninduced cells. We also found, by reverse transcriptase, that the second putative promoter is not functional under normal or stress con ditions, and the amount of mRNA was found to be proportional to active MnSOD. Thus, these results indicate that under oxidative stress/induc ing conditions, the increase in aerobic transcription of sodA occurs f rom only one transcription start site without affecting the stability of sodA mRNA. In addition, the 1:1 ratio found between increases in so dA mRNA and active MnSOD suggests that no translational regulation occ urs aerobically.