This is the N-terminal domain found in DraK Histidine Kinase (HK) present in Streptomyces coelicolor. Activation of the DraK HK leads to autophosphorylation of its kinase domain in the cytoplasm and subsequent transphosphorylation of DraR promoting blue-pigmented polyketide actinorhodin (ACT) production. The N-terminal domain is known as the sensor (or input) domain and undergoes a conformational change resulting in phosphorylation of a conserved histidine in its cytoplasmic kinase domain [1].

1: Mechanism of the pH-induced conformational change in the sensor domain of the DraK Histidine kinase via the E83, E105, and E107 residues. Yeo KJ, Hong YS, Jee JG, Lee JK, Kim HJ, Park JW, Kim EH, Hwang E, Kim SY, Lee EG, Kwon O, Cheong HK; PLoS One. 2014;9:e107168. PMID:25203403