A calcium reporter protein that exhibits superior fluorescence properties and calcium reactivity is obtained by providing DNA in which one nucleotide among the nucleotide coding the calmodulin-binding sequence (ckkap sequence) of the calcium/calmodulin- dependent protein kinase kinase and the nucleotide coding the calcium-binding sequence (CaM sequence) of calmodulin is bonded to the 5 terminal side of a nucleotide coding a fluorescent protein, and the other nucleotide thereamong is bonded to the 3 terminal side of the nucleotide coding a fluorescent protein. The calcium reporter protein coded by this DNA exhibits superior fluorescence properties and calcium reactivity in comparison to existing calcium reporter proteins due to having the ckkap sequence as a binding domain for CaM sequences to which calcium has bonded.
