TRANSLATION OF THE ADHE TRANSCRIPT TO PRODUCE ETHANOL DEHYDROGENASE REQUIRES RNASE-III CLEAVAGE IN ESCHERICHIA-COLI

Previous studies have shown that the adhE gene, which encodes a multif unctional protein with ethanol dehydrogenase activity, is under transc riptional regulation. The level of dehydrogenase activity in cells gro wn fermentatively is about 10-fold higher than that in cells grown aer obically. In these studies, we mapped the promoter to a region well up stream of the protein-coding region of adhE. Unexpectedly, in mutants lacking the endoribonuclease]RNase III, no significant ethanol dehydro genase activity was detected in cells grown anaerobically on rich (Lur ia-Bertani) medium supplemented with glucose, even though adhE mRNA le vels were high. Indeed, like Delta adhE mutants, strains lacking RNase III failed to grow fermentatively on glucose but grew on the more oxi dized carbon source glucuronate, Computer-generated secondary structur es of the putative 5' untranslated region of adhE mRNA suggest that th e ribosome binding site is occluded by intramolecular base pairing, It seems likely that cleavage of this secondary structure by RNase III i s necessary for efficient translation initiation.