PURPOSE: To obtain a DNA fragment, containing a specific DNA fragment, having the promoter function in a bacterium belonging to the genus Thermus, suitable for breeding highly thermophilic bacterium of the genus Thermus and expressing a useful gene using the bacterium as a host at a high efficiency and useful for the production, etc., of a thermostable protein. CONSTITUTION: This DNA fragment contains one or more DNA fragments selected from the group consisting of a DNA fragment derived from a chromosomic DNA of a bacterium belonging to the genus Thermus represented by a base sequence of formula I or II, etc., and has the promoter function in the bacterium belonging to the genus Thermus. Furthermore, the DNA fragment is obtained by extracting a chromosomic DNA from a cultured product of, e.g. a Thermus thermophilus HB27 strain, carrying out the ultrasonic crushing treatment of the resultant chromosomic DNA, then recovering a fraction containing a DNA fragment of about 200bp average size, providing flush ends in the terminals of the recovered DNA fragment and subsequently joining a restriction enzyme linker such as EcoRI thereto.
