Thermostable ribonuclease H from

1. An isolated nucleic acid encoding a polypeptide having a thermostable ribonuclease H activity, said nucleic acid being selected from the group consisting of:

(a) a nucleic acid encoding a polypeptide having the amino acid sequence of SEQ ID NO: 1;

(b) a nucleic acid encoding a polypeptide having an amino acid sequence that shares at least 85% identity with the amino acid sequence of SEQ ID NO: 1;

(c) a nucleic acid having the nucleotide sequence of SEQ ID NO: 2;

(d) a nucleic acid capable of hybridizing to the nucleic acid consisting of the nucleotide sequence of SEQ ID NO:2 or the full-length complementary strand thereof under conditions of incubation in 6×SSC (1×SSC: 0.15 M NaCl, 0.015 M sodium citrate, pH 7.0) containing 0.5% SDS, 0.1% bovine serum albumin (BSA), 0.1% polyvinylpyrrolidone, 0.1% Ficoll 400 and 0.1% denatured salmon sperm nucleic acid at 50° C. for 20 hours, and washing in 2×SSC containing 0.5% SDS at 37° C. while changing the SSC concentration down to 0.1×SSC and the temperature up to 50° C.; and

(e) a nucleic acid having a nucleotide sequence that shares at least 90% identity with the nucleotide sequence of SEQ ID NO: 2,

wherein said nucleic acid is endogenously found in organisms from the genus Archaeoglobus , which is amplified by PCR using primers having nucleic acid sequences of SEQ ID NO: 8 and SEQ ID NO: 9 and 40 cycles of 94° C. for 30 seconds, 55° C. for 30 seconds and 72° C. for 1 minute.

2. A recombinant DNA comprising the nucleic acid of claim 1 .

3. An isolated transformant transformed with the recombinant DNA of claim 2 .

4. A method for producing a polypeptide having a thermostable ribonuclease H activity, the method comprising:

culturing the transformant of claim 3 ;

and collecting a polypeptide having a thermostable ribonuclease H activity from the culture.