Universal Relationship in Gene-Expression Changes for Cells in Steady-Growth State

Cells adapt to different conditions by altering a vast number of components, which is measurable using transcriptome analysis. Given that a cell undergoing steady growth is constrained to sustain each of its internal components, the abundance of all the components in the cell has to be roughly doubled during each cell-division event. From such steady-growth constraint, expression of all genes is shown to change along a one-parameter curve in the state space in response to the environmental stress. This conclusion leads to a global relationship that governs the cellular state: By considering a relatively moderate change around a steady state, logarithmic changes in expression are shown to be proportional across all genes, upon alteration of stress strength, with the proportionality coefficient given by the change in the growth rate of the cell. This theory is confirmed by transcriptome analysis of Escherichia coli in response to several stresses