Congruence between noise and plasticity in protein expression.

Gene expression responds to various types of perturbations, such as mutations, environmental changes, and stochastic molecular noises. These different types of variability are often interdependent, where genes sensitive to one perturbation tend to be sensitive to others. However, the relationship between plasticity (variability in response to environmental changes) and noise (variability among cells under the same conditions) in gene expression remains debatable. Previous studies predicted a positive correlation between plasticity and noise in nonessential genes, but these were often measured at different levels: plasticity at the mRNA level and noise at the protein level. This methodological discrepancy complicates the understanding of their relationship. We addressed this by measuring protein expression in Escherichia coli, quantifying both plasticity and noise from the same dataset using flow cytometry. Essential genes exhibited lower noise and plasticity than nonessential genes. Nonessential genes showed a positive correlation between noise and plasticity, while essential genes did not. This study provides empirical evidence of essentiality-dependent coupling between noise and plasticity in protein expression, highlighting the organization of different types of variabilities.