Resource Competition

Resource Competition is the coupling between co-expressed genes that arises because they share a finite pool of cellular resources, principally ribosomes and RNA polymerase, causing the expression of one gene to influence the expression of others ¹.

How It Works

Every gene expressed in a cell consumes ribosomes for translation and RNA polymerase for transcription. When multiple genes or circuits are active simultaneously, they draw from the same limited pools. Increasing expression of one gene sequesters more ribosomes, leaving fewer available for other genes. This creates an indirect negative coupling between all expressed genes.

Resource competition manifests as unexpected behaviors in synthetic circuits. A simple example is when inducing one gene on a plasmid causes a decrease in expression of an unrelated co-expressed gene, even though no designed regulatory interaction exists between them. This coupling can corrupt logic gate behavior, create false positive feedback, or destabilize oscillators.

The severity of resource competition depends on total expression load relative to resource supply. Cells growing rapidly have more ribosomes and tolerate higher expression loads. Overloaded cells exhibit global expression depression and growth rate reduction, linking resource competition to host burden.

Computational Considerations

Resource-aware modeling frameworks extend standard ODE models by explicitly tracking free ribosome and RNAP concentrations as shared variables. The isocost line framework provides an intuitive geometric description of how total protein output is distributed among competing genes. These models predict emergent coupling and guide resource-efficient circuit designs that minimize unintended interactions ².

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