Effects of Resource Sharing on Gene Expression Dynamics

Caveney, P. M., University of Tennessee Knoxville
Simpson, M. L., Oak Ridge National Laboratory
Chin, C., University of Tennessee Knoxville
Collier, C. P., Oak Ridge National Laboratory
Retterer, S. T., Oak Ridge National Laboratory

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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