Molecular model of Heterosigma akashiwo Trg1. Structural model of the DNA recognition domain of Trg1 (shown in yellow) based on the defined partial structures of Escherichia coli OmpR (grey), PhoB (white), and the complete receiver-regulator structure from Thermotoga maritima (blue) reveals important similarities. The predicted Trg1 model closely resembles that of OmpR, particularly in the putative DNA binding region (α3 helix). Notably, the predicted Trg1 structure for the putative RNA polymerase interaction site (α2-α3 loop, red) more closely matches that of PhoB. The phosphorylation site is shown as a purple sphere.