The han1A gene, encoding a subunit of the histone-like protein HAN1 from the Thermococcus species AN1, has been cloned and sequenced. Sequence analysis of the translation product of the gene demonstrates homology with other archaeal histone-like proteins of the 'HMf family' and eukaryal consensus sequences, particularly H4. The region of highest homology between the AN1 histone subunit, termed the HAN1A1 subunit, and the H4 consensus is suggested, by the 3-dimensional structure of the histone octamer, to interact with the minor groove of DNA. The results presented add further weight to the notion that the 'archaeal histones' and the eukaryal histones are indeed related and that the approximate 65 amino acid residue length of the archaeal histones represents the archaeal equivalent of the histone fold structural building block common to all eukaryal histones.