To provide a promoter, a recombinant DNA, a gene expression vector, an expression vector, and a transformant, which are capable of expressing a gene without inducing gene expression with an inducer; and a method for producing a protein and a kit therefor, which can be operated easily and performed inexpensively by convenient and inexpensive steps. An isolated DNA having the nucleotide sequence of SEQ ID NO: 1 or 2 of Sequence Listing or a fragment thereof, wherein the isolated DNA exhibits a constitutive promoter activity in Escherichia coli or a bacterium belonging to the genus Bacillus; an isolated DNA having a nucleotide sequence of a nucleic acid capable of hybridizing to the above DNA, wherein the isolated DNA exhibits a constitutive promoter activity in Escherichia coli or a bacterium belonging to the genus Bacillus; a recombinant DNA comprising the above DNA and a foreign gene, wherein the foreign gene is operably located; a gene expression vector, at least comprising the above DNA; an expression vector comprising the recombinant DNA; a transformant having the above recombinant DNA, or the above expression vector; a method for producing a protein, characterized by culturing the above transformant, and collecting a protein from the resulting culture; and a kit for producing a protein, at least comprising the above DNA, or the above gene expression vector.