GENETIC-RECOMBINATION OF BACTERIAL PLASMID DNA - PHYSICAL AND GENETIC-ANALYSIS OF THE PRODUCTS OF PLASMID RECOMBINATION IN ESCHERICHIA-COLI

[摘要] Derivatives of plasmid pBR322 DNA containing tet mutations were constructed by inserting XhoI linkers at various sites in the tetracycline resistance gene. Monomer plasmids containing the tet-10 allele located at nucleotide position 23 or the tet-14 allele located at nucleotide position 1267 were used to construct a circular dimer containing 1 copy of each allele and a circular trimer containing 1 copy of the tet-10 allele and 2 copies of the tet-14 allele. Genetic recombination of these plasmid DNAs to produce a functional tetracycline resistance gene could be detected as the production of tetracycline-resistant progeny during the growth of transformants or using a restriction mapping assay which detected the rearrangement of the mutant alleles. The structure of individual tetracycline-resistant recombination products was determined by restriction mapping. This analysis suggested that as many as 70% of the plasmid recombination events in E. coli AB1157 could have involved gene conversion events. The formation of these recombination products was most easily predicted by a model involving figure 8 recombination intermediates and the formation of symmetric regions of heteroduplex. Recombination in JC10287 .DELTA.(srlR-recA)304 occurred at 5% of the wild-type frequency and appeared to occur by a similar mechanism. Recombination in JC9604 recA56 recB21 recC22 sbcA23 occurred at 20 times the wild-type frequency and appeared to involve multiple independent recombination events.