The coordinated action of RNase III and RNase G controls enolase expression in response to oxygen availability in Escherichia coli

Rapid modulation of RNA function by endoribonucleases during physiological responses to environmental changes is known to be an effective bacterial biochemical adaptation. We report a molecular mechanism underlying the regulation of enolase (eno) expression by two endoribonucleases, RNase G and RNase III, the expression levels of which are modulated by oxygen availability in Escherichia coli. Analyses of transcriptional eno-cat fusion constructs strongly suggested the existence of cis-acting elements in the eno 5' untranslated region that respond to RNase III and RNase G cellular concentrations. Primer extension and S1 nuclease mapping analyses of eno mRNA in vivo identified three eno mRNA transcripts that are generated in a manner dependent on RNase III expression, one of which was found to accumulate in rng-deleted cells. Moreover, our data suggested that RNase III-mediated cleavage of primary eno mRNA transcripts enhanced Eno protein production, a process that involved putative cis-antisense RNA. We found that decreased RNase G protein abundance coincided with enhanced RNase III expression in E. coli grown anaerobically, leading to enhanced eno expression. Thereby, this posttranscriptional up-regulation of eno expression helps E. coli cells adjust their physiological reactions to oxygen-deficient metabolic modes. Our results revealed a molecular network of coordinated endoribonuclease activity that post-transcriptionally modulates the expression of Eno, a key enzyme in glycolysis.