The article reviews the main systems that regulate gene expression in cyanobacteria in response to various treatments: low and high temperatures, salt, hyperosmotic and oxidative stresses. The systems for perception of light are also reviewed. Functional characteristics are presented for known two-component regulatory systems, eukaryotic-type serine-threonine protein kinases, σ-subunits of RNA-polymerase, DNA-binding transcription factors. Different mechanisms of perception of stress signals are analyzed, including changes in DNA supercoiling under different stress conditions. [ABSTRACT FROM AUTHOR]