Archaeal integrases facilitate the formation of two distinctive types of integrated element within archaeal chromosomes: the SSV type and pNOB8 type. The former carries a smaller N-terminal and a larger C-terminal integrase gene fragment, and the latter an intact integrase gene. All integrated elements overlap tRNA genes that were target sites for integration. It has been demonstrated that SSV (Sulfolobus spindle virus) viruses, carrying an SSV-type integrase gene, and conjugative plasmids, carrying a pNOB8-type integrase, are integrative elements. Two mechanisms have been proposed for stably maintaining an integrated element within archaeal chromosomes. There is also evidence for changes having occurred in the captured integrated elements present in archaeal genomes. Thus we infer that site-specific integration constitutes an important mechanism for horizontal gene transfer and genome evolution.

Abbreviations used:attB, attachment site of host chromosome; attL, attachment site at left integration border; attR, attachment site at right integration border; attP, attachment site of genetic element; HGT, horizontal gene transfer; int, integrase gene; intN and intC, N-terminal and C-terminal part of integrase gene; ORF, open reading frame; SSV, Sulfolobus spindle virus.

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Author notes

Thermophiles 2003, a held at University of Exeter, 15–19 September 2003

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Permanent address: Department of Microbiology, College of Life Sciences, Nanjing Agricultural University, Nanjing, People's Republic of China.