  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 this 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 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.
