A putative two‐component signal transduction system regulates σ E , a sigma factor required for normal cell wall integrity in Streptomyces coelicolor A3(2)

The extracytoplasmic function (ECF) sigma factor, σ E , is required for normal cell wall integrity in Streptomyces coelicolor . We have investigated the regulation of σ E through a transcriptional and mutational analysis of sigE and the surrounding genes. Nucleotide sequencing identified three genes located downstream of sigE  ; orf202 , cseB and cseC ( cse , c ontrol of s ig E  ). cseB and cseC encode a putative response regulator and a putative transmembrane sensor histidine protein kinase respectively. Although most sigE transcription appeared to be monocistronic, sigE was also transcribed as part of a larger operon, including at least orf202. sigE null mutants are sensitive to cell wall lytic enzymes, have an altered peptidoglycan muropeptide profile, and on medium deficient in Mg 2+ they overproduce actinorhodin, sporulate poorly and form crenellated colonies. A constructed cseB null mutant appeared to have the same phenotype as a sigE null mutant, which was accounted for by the observed absolute dependence of the sigE promoter on cseB . It is likely that the major role of cseB is to regulate sigE transcription because expression of sigE alone from a heterologous promoter suppressed the cseB mutation. Mg 2+ suppresses the CseB/SigE phenotype, probably by stabilizing the cell envelope, and sigE transcript levels were consistently higher in Mg 2+ ‐deficient cultures than in high Mg 2+ ‐grown cultures. We propose a model in which the CseB/CseC two‐component system modulates activity of the sigE promoter in response to signals from the cell envelope.