An isolated or synthesized gene encoding a protein comprising the amino acid sequence represented by SEQ ID NO:2; an isolated or synthesized gene encoding a protein comprising an amino acid sequence derived from the amino acid sequence represented by SEQ ID NO:2 by the deletion, substitution or addition of one or more amino acids and being capable of regenerating luciferin; an isolated or synthesized gene encoding a protein being hybridizable with the complementary sequence of a DNA comprising the base sequence represented by SEQ ID NO:1 under stringent conditions and capable of regenerating luciferin; a recombinant DNA characterized by having an isolated or synthesized gene as described above inserted into a vector DNA; a transformant or a transductant containing the above recombinant DNA; and a process for producing a protein capable of regenerating luciferin characterized by comprising culturing the above transformant or transductant in a medium and collecting the protein capable of regenerating luciferin from the culture.