Real-time observation of bacterial gene expression noise

The mRNA variability in the single cells attributes to random periods of transcription bursts. The cell cycle possesses a global role in affecting transcriptional output. By expressing this process as a communication system at the nanoscale, this transcription output often accounts for the gene expression noise, and this quantifies the promoter activity. However, current stochastic models ignore the fact that gene expression noise is affected not only by the cell cycle and promoter activity, but, also, by the time during which new mRNAs are produced. Here we show that noise from the lac promoter in E.coli is dominated by intrinsic and extrinsic noises in slow and fast dividing cells, respectively. Such domination of the noise components in phases with different generation times is achieved through distinct and combinatorial interactions between the upstream/downstream regulatory elements. These mechanisms serve as an adaptive strategy for increasing population homogeneity under changing environments.