Japanese pNOB8 (4l kbp) and the Icelandic pING 1 (25 kbp) were sequenced. About half of the sequence of pING1 strongly resembles about a third of pNOB8. The rest of the sequences is quite different. Two related ORFs highly conserved in these plasmids show weak but at least for one of them significant similarity to genes of bacterial conjugative systems. The putative homologs of both are ATPases probably involved in plasmid transfer. At least parts of archaeal and bacterial conjugation systems might thus be derived from common ancestral modules. The analysis of the sequences also yielded hints on plasmid maintenance and on the frequent formation of variants by recombination. Incomplete variants allow a partial dissection of functions.
The self spreading nature of both the viruses, particularly of SSV 1 which, in addition, stably integrates into the host chromosome, and the conjugative plasmids makes both good candidates for developing self selecting cloning and/or expression vectors as part of a genetic system for Sulfolobus.
