Growth phase-dependent ribonucleic acid production dynamics

Transcriptional events play a crucial role in major cellular processes that specify the activity of an individual cells and influences cell population behavior in response to environment. Active (ON) and an inactive (OFF) states controls the transcriptional burst. Yet, the mechanism and kinetics of ON/OFF-state across the different growth phases of Escherichia coli remains elusive. Here, we have used a single mRNA detection method in live-cells to comprehend the ON/OFF mechanism of the first transcriptional (T_F) and consecutive events (T_C) controlled by lactose promoters, P_lac and P_lac/ara1. We determined that the duration of T_F ON/OFF has different modes, exhibiting a close to inverse behavior to that of T_C ON/OFF. Dynamics of ON/OFF states in fast and slow-dividing cells were affected by the promoter region during the initiation of transcription. Period of T_F ON-state defines the behavior of T_C by altering the number and the frequency of mRNAs formed. Furthermore, we have shown that delayed OFF-time in T_F affects the dynamics of T_C in both states_, which is mainly determined by the upstream promoter region. Furthermore, using elongation arrest experiments, we independently validate that mRNA noise in T_C is governed by the delayed OFF-period in T_F. We have identified the position of the regulatory regions that plays a crucial role in noise (Fano) modulation. Taken together, our results suggest that the dynamics of the first transcriptional event, T_F, pre-defines the diversity of the population.