title: Trans-complementation-dependent replication of a low molecular weight origin fragment from plasmid R6K.
abstract: A non-self-replicating segment (1370 base pairs) of plasmid R6K was cloned in E. coli and shown to trans-complement temperature-sensitive replication mutants of this plasmid. This segment contains the gene which codes for a protein required for initiation of replication of the plasmid, and was used as a helper in a functional assay for an origin of replication in R6K derivatives. A 420 bp fragment, derived from R6K DNA, was shown to carry a functional origin since it was capable of replicating as a plasmid in E. coli cells carrying the helper segment either on the host chromosome or on a plasmid Col E1 derivative. The copy number of the origin fragment in cells carrying the helper segment on the chromosome is essentially the same as the copy number of R6K. A model for the positive regulation of plasmid R6K replication is presented.
mesh_terms: D002874:Chromosome Mapping; D003090:Coliphages / Q000235:genetics; D004261:DNA Replication; D005816:Genetic Complementation Test; D009154:Mutation; D011815:R Factors