A histone-like gene, PHS051 from hyperthermophilic archaeon Pyrococcus horikoshii OT3 strain, was cloned, sequenced, and expressed in Escherichia coli. The recombinant histone, HPhA, encodes a protein of 70 amino acids with a molecular weight of 7868 Da. Amino acid sequence analysis of HPhA showed high homology with other archaeal histones and eukaryal core histones. The HPhA was purified to homogeneity by heat precipitation and affinity chromatography. Gel electrophoresis mobility shift assays demonstrate that the purified HPhA has high affinity to DNA. The complex of the HPhA and DNA allows DNA to be protected from cleavage by the restriction enzyme TaqI at 65 degreesC. Circular dichroism spectra reveal that the conformation of the recombinant historic HPhA becomes looser when temperatures increase from 25 to 90 degreesC. The HPhA has inherited a remarkable thermostability especially in the presence of 1 M KCI and retained DNA binding activity at extreme temperature, which is consistent with our previous report about its structure stability analyzed by X-ray crystallography. (C) 2003 Elsevier Inc. All rights reserved.