Effects of Resource Sharing on Gene Expression Dynamics

Gene expression is a noisy process¹, and a large portion of expression noise is bursting, where many proteins are made in short bursts punctuated by periods of no expression². Many sources of bursting have been investigated (e.g. supercoiling³ and transcription factors⁴), but the possible utility of bursting vis-à-vis resource sharing is not well understood. Here we explore how recyclable resources (e.g. polymerase and ribosomes) are temporally shared among actively expressing genes. By confining reactions to cell-sized PDMS chambers and POPC vesicles, we compare how resources are shared when they are either partitioned experimentally or naturally by the genes themselves. We find that resources are shared in a bursty manner (i.e. few genes have many resources for brief periods of time), and surprisingly, chambers with higher protein abundance increase the size bursts instead of initiating more frequent bursts. This is likely due to the difficulty in assembling the ~100 components necessary for protein expression⁵. Once assembled, the components are spatially correlated and thus have a higher probability of rebinding than if the solution were well mixed⁶. We corroborate our results with a simple model in which genes that transcribe mRNA early gather a disproportionate share of the protein expression resources resulting in a larger burst of protein expression. Our results further the understanding of burst frequency saturation⁷ and important cell-fate decisions⁸.

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