General genetic recombination of bacterial plasmids.

Abstract

Analysis of genetic recombination between 2 chromosomes, which differ from each other by at least 2 genetic markeŕs, is based mainly on the production of recombinants which are phenotypically distinguishable from their progenitors. The use of small DNA molecules such as bacterial plasmids as recombination substrates provides an additional handle for the investigation of recombination. It also allows the description of recombination events in molecular terms. Recombination of 2 plasmids, genetically distinguishable from each other, can be followed as recombination reactions in other systems by monitoring changes in the phenotypic expression of the plasmid genes (1,2,3). But in addition, plasmidic recombination may be investigated by analyzing changes of their molecular structures. Interplasmidic recombination leads to the formation of plasmid oligomers and intraplasmidic recombination between repeated sequences can lead to deletion of the region between the crossing-over sites, and, when the recombination substrate is an oligomer, to monomerization. When mutations affect restriction endonuclease sites, recombination products may be compared to recombination substrates by restriction endonculease analysis (2,4,5). The small size of bacterial plasmids also allows the isolation and characterization of molecular intermediates of the recombination pathway (6,7).