Burst Kinetics
Also known as: transcriptional bursting, expression bursting
The phenomenon where genes produce mRNA and protein in stochastic pulses rather than at constant rates.
Burst Kinetics describes the stochastic, pulsatile nature of gene expression where mRNA and protein molecules are produced in discrete bursts separated by inactive periods, rather than at a smooth continuous rate 1.
How It Works
Transcriptional bursting arises because promoters stochastically switch between active (ON) and inactive (OFF) states. During an ON period, RNA polymerase initiates multiple rounds of transcription producing a burst of mRNA molecules. During OFF periods, no new transcripts are made. Each mRNA molecule is then translated in a burst of protein molecules before being degraded.
Burst frequency is determined by the rate at which a promoter transitions from OFF to ON, while burst size depends on how many transcripts are produced per ON period and how many proteins are translated per transcript. Together these parameters set both the mean expression level and the noise characteristics of a gene.
The biological consequences of bursting are significant. Genetically identical cells in a uniform environment can show wide variation in protein levels, creating phenotypic heterogeneity. This variation can be functionally important for bet-hedging strategies, antibiotic persistence, and cellular differentiation.
Computational Considerations
The two-state promoter model is the standard framework for analyzing burst kinetics, using stochastic simulation algorithms such as the Gillespie algorithm to generate expression trajectories. Analytical solutions for burst size and frequency distributions enable fitting to single-cell fluorescence data. These models reveal how circuit architecture, promoter design, and feedback loops shape noise properties 2.
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Stochastic simulation algorithms model burst frequency and size distributions to predict cell-to-cell variability in gene expression from circuit architectures.