Added value of autoregulation and multi-step kinetics of transcription initiation

Optimal transition paths of phenotypic switching in a non-Markovian self-regulation gene expression

Gene expression is a complex biochemical process involving multiple reaction steps, creating molecular memory because the probability of waiting time between consecutive reaction steps no longer follows exponential distributions. What effect the molecular memory has on metastable states in gene expression remains not fully understood. Here, we study transition paths of switching between bistable states for a non-Markovian model of gene expression equipped with a self-regulation. Employing the large deviation theory for this model, we analyze the optimal transition paths of switching between bistable states in gene expression, interestingly finding that dynamic behaviors in gene expression along the optimal transition paths significantly depend on the molecular memory. Moreover, we discover that the molecular memory can prolong the time of switching between bistable states in gene expression along the optimal transition paths. Our results imply that the molecular memory may be an unneglectable factor to affect switching between metastable states in gene expression.

Efficiency and Robustness of Processes Driven by Nucleoid Exclusion in Escherichia coli

The internal spatial organization of prokaryotic organisms, including Escherichia coli, is essential for the proper functioning of processes such as cell division. One source of this organization in E. coli is the nucleoid, which causes the exclusion of macromolecules - e.g. protein aggregates and the chemotaxis network - from midcell. Similarly, following DNA replication, the nucleoid(s) assist in placing the Z-ring at midcell. These processes need to be efficient in optimal conditions and robust to suboptimal conditions. After reviewing recent findings on these topics, we make use of past data to study the efficiency of the spatial constraining of Z-rings, chemotaxis networks, and protein aggregates, as a function of the nucleoid(s) morphology. Also, we compare the robustness of these processes to nonoptimal temperatures. We show that Z-rings, Tsr clusters, and protein aggregates have temperature-dependent spatial distributions along the major cell axis that are consistent with the nucleoid(s) morphology and the volume-exclusion phenomenon. Surprisingly, the consequences of the changes in nucleoid size with temperature are most visible in the kurtosis of these spatial distributions, in that it has a statistically significant linear correlation with the mean nucleoid length and, in the case of Z-rings, with the distance between nucleoids prior to cell division. Interestingly, we also find a negative, statistically significant linear correlation between the efficiency of these processes at the optimal condition and their robustness to suboptimal conditions, suggesting a trade-off between these traits.