Photosensitive kinase and response regulator that is involved in increased bacterial virulence upon exposure to light. ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. Constitutively expressed when grown in minimal media. FMN binds covalently to cysteine after exposure to blue light and this bond is spontaneously broken in the dark. Treatment of phosphorylated protein with alkaline buffer to hydrolyze phospho-aspartates does not significantly reduce phosphorylation in assays performed in vitro. Therefore, it is not clear whether Asp-461 is really phosphorylated by His-164.