CHASE9 is a conserved extracellular (periplasmic) sensor domain found in histidine kinases, diguanylate cyclases/phosphodiesterases, methyl-accepting chemotaxis proteins, adenylate cyclases and protein serine phosphatases, including the c-di-GMP phosphodiesterases PdeI (YliE) of Escherichia coli [1].

1: Systematic Nomenclature for GGDEF and EAL Domain-Containing Cyclic Di-GMP Turnover Proteins of Escherichia coli. Hengge R, Galperin MY, Ghigo JM, Gomelsky M, Green J, Hughes KT, Jenal U, Landini P; J Bacteriol. 2015;198:7-11. PMID:26148715