Effects of Mg(2+) on in vivo transcriptional dynamics of the lar promoter.

In vitro studies show that the transcriptional dynamics in Escherichia coli is sensitive to Mg(2+) concentration in the cell. We study in vivo how Mg(2+) affects the production of RNA molecules under the control of the lar promoter, P(lar), a lac promoter variant. The target RNA codes for RFP followed by 96 MS2d-GFP binding sites, allowing in vivo detection of individual RNA molecules following transcription. As Mg(2+) concentration is increased, transcripts' production first increases, but then decreases. Results were confirmed by qPCR and gel assay. Analysis of cell to cell diversity in RNA production shows that the variance of RNA numbers changes with Mg(2+). Gel assay confirms changes in the structure of the target RNA. These results suggest that changes in the dynamics of elongation may also affect RNA production, along with changes in the dynamics of the promoter open complex. The findings suggest that changes in metabolite concentration can have multiple, complex effects on the in vivo dynamics of transcription. Comparative analysis of the effects on the dynamics of transcription of other metabolites confirms the significance of the effects of Mg(2+) ions. Namely, we show that Ca(2+) and Fe(2+) have almost negligible effects in comparison to Mg(2+).