The complete sequence of the 5350-bp plasmid pRN1 from the crenarchaeo
te Sulfolobus islandicus has been determined. This plasmid is the firs
t 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 fra
mes, including one that spans over half the plasmid and has significan
t similarity to the helicase domain of viral primase proteins. Directl
y upstream of this putative primase is a homologue of Cop, a family of
small proteins from promiscuous eubacterial plasmids which control co
py number by repressing the expression of the replication initiation p
rotein. In eubacterial plasmids cop is found upstream of the replicati
on initiator protein, The location of a cop homologue upstream of a pr
imase-like gene in pRN1 suggests that it controls DNA replication in a
manner similar to these eubacterial plasmids, but does so using a mix
ture of componants from plasmids and viruses. (C) 1996 Academic Press,
Inc,