Mode of replication of plasmid lambda-dv-1.

About 20 copies of plasmid lambda-dv are perpetuated per host chromosome in Escherichia coli K12 cells. The mode of DNA replication of this plasmid lambda-dv was studied, using the density-labelling technique followed by banding in DsCl. It was shown that all the copies of plasmid lambda-dv are potentially capable of replicating roughly once a cell generation. Their replication occurs by random, that is a copy of the plasmid is taken out at random for replication from a pool, to which the two replicas resulting from replication are returned. Chloramphenicol did not inhibit the initiation of a new round of replication of the plasmid molecules, indicating that selection from the replication pool does not require concomitant protein synthesis.