Complete nucleotide sequence of the Sulfolobus islandicus multicopy plasmid pRN1

The complete sequence of the 5350-bp plasmid pRN1 from the crenarchaeote Sulfolobus islandicus has been determined. This plasmid is the first to be sequenced from this group of thermoacidophilic archaebacteria (Archaea) and its high copy number and wide host range make it a good candidate for a cloning vector. pRN1 contains several open reading frames, including one that spans over half the plasmid and has significant similarity to the helicase domain of viral primase proteins. Directly upstream of this putative primase is a homologue of Cop, a family of small proteins from promiscuous eubacterial plasmids which control copy number by repressing the expression of the replication initiation protein. In eubacterial plasmids cop is found upstream of the replication initiator protein. The location of a cop homologue upstream of a primase-like gene in pRN1 suggests that it controls DNA replication in a manner similar to these eubacterial plasmids, but does so using a mixture of components from plasmids and viruses.