Global Regulatory Systems

Cells use global regulatory systems to respond to environmental changes by linking sensory input with gene expression.

Regulons are groups of genes and operons regulated by a single global regulator, like the cAMP receptor protein, or CRP, that regulates the lac and ara operons to use non-glucose sugars efficiently.

Bacteria also employ two-component signaling systems, like the EnvZ/OmpR system, which comprises a sensor kinase and a response regulator.

When osmolarity changes, the sensor kinase EnvZ undergoes autophosphorylation and transfers the phosphate group to the cytoplasmic response regulator, OmpR.

OmpR then differentially regulates the ompF and ompC gene expression, adjusting the porin type for membrane permeability.

Sigma factors guide RNA polymerase to specific promoters for rapid gene expression changes. For example, σ32 activates heat-shock genes to combat thermal stress, while σS regulates stationary-phase survival.

Secondary messengers are small molecules that amplify external signals to regulate diverse cellular processes. For example, cAMP regulates carbon utilization genes via CRP.