Identification of a thermophilic plasmid origin and its cloning within a new Thermus-E. coli shuttle vector.

A pUC19-based vector has been generated for selecting functional thermophilic origins (oris) of Thermus ssp. Once combined with thermophilic DNA, the vector can be amplified in ampicillin resistant (Ap(R)) E. coli, prior to transformation and kanamycin (Km) selection in Thermus thermophilus. The Km(R) Thermus transformants replicate any newly-formed shuttle vectors via introduced thermophilic oris. Using this "ori-selecting" vector, three novel thermophilic oris were cloned from randomly digested Thermus cryptic plasmid DNA. These shuttle vectors are useful for genetic analyses, as well as protein engineering within thermophiles. The smallest ori-containing sequence of 4.2 kb has been subcloned, sequenced, and further refined to 2.3 kb. A significant ORF of 341 amino acids (aa), with a Thermus promoter and RBS, is found within the thermophilic ori. Deleting part of this ORF abolishes the shuttle vector's ability to replicate in T. thermophilus. Therefore, we postulate that this ORF encodes a replication protein (Rep) necessary for thermophilic plasmid replication. The thermophilic ori also contains two sequences which resemble DnaA boxes.