[Transmissible hybrid plasmid RP4-ColE1].

Hybrid plasmid RP4-ColE1 was obtained by joining DNA plasmids RP4 and ColE1, each of which possessed only one site of restriction for EcoR1. These plasmid molecules were restricted by endonuclease EcoR1 and then treated by ligase. The hybrid plasmid retained the property of transmissibility typical for drug factor resistance RP4. Non-transmissible mutant of the hybrid plasmid selected by the character of the resistance of Escherichia coli C600 (RP4-ColE1) to the phage PRR1 is used for subsequent investigations.