Characterizing the dynamics of specific RNA levels requires realtime
RNA profiling in a single cell. We show that the combination
of a synthetic modular genetic system with fluorescence correlation
spectroscopy allows us to directly measure in real time the
activity of any specific promoter in prokaryotes. Using a simple
inducible gene expression system, we found that induced RNA
levels within a single bacterium of Escherichia coli exhibited a
pulsating profile in response to a steady input of inducer. The
genetic deletion of an efflux pump system, a key determinant of
antibiotic resistance, altered the pulsating transcriptional dynamics
and caused overexpression of induced RNA. In contrast with
population measurements, real-time RNA profiling permits identifying
relationships between genotypes and transcriptional dynamics
that are accessible only at the level of the single cell.
