THE ALDA-GENE OF ESCHERICHIA-COLI IS UNDER THE CONTROL OF AT LEAST 3 TRANSCRIPTIONAL REGULATORS

Expression studies on the aldA gene encoding aldehyde dehydrogenase in Escherichia coli showed induction by two types of molecule (hydroxyal dehydes and 2-oxoglutarate), carbon catabolite repression and respirat ion dependence. Promoter deletion analysis showed that the proximal op erator, which includes inducer-regulator complex and catabolite repres sion protein (Crp) recognition sites, was necessary for induction by e ither type of inducer, and that full induction by aldehydes required t he cooperation of distal operator sequences beyond position -119. Inte ractions of the regulator protein with the -59 to -6 fragment were sho wn by DNA mobility shift assays. Fusions of different deletions of the aldA promoter to lacZ indicated that a Crp site proximal to the trans criptional start point (tsp) was functional in the cAMP-dependent cata bolite repression of this system, whereas a distal control site was li kely to operate in a cAMP-independent catabolite repression. DNA mobil ity shift and footprint analyses showed that only the tsp proximal sit e was bound by pure Crp with a K-d of 5.4 x 10(-7) M. As shown by an A re-defective strain, the aldA gene seems to be repressed by the Are sy stem under anaerobiosis, displaying its physiological full induction a nd activity in the presence of oxygen.