ABSTRACT
Recombination between the IS50 sequences that flank Tn5 has been found to occur readily after the transformation of E. coli recA strains with a plasmid that contains direct repeats of these sequences. Analysis of mutants of IS50 indicates that the polypeptide encoded by IS50 that is required for transposition is also required for the recombination. Surprisingly, the mechanism of recombination appears to be similar to general homologous recombination rather than site-specific recombination. This IS50 recombination system may be responsible for resolving transient cointegrate structures containing direct repeats of IS50 or Tn5 during the transposition of IS50 and Tn5.
Subject(s)
Bacterial Proteins/genetics , Recombination, Genetic , DNA, Bacterial/metabolism , Escherichia coli/genetics , Mutation , Plasmids , Rec A Recombinases , Repetitive Sequences, Nucleic AcidABSTRACT
The structures of three recombinants between bacteriophage lambda DNA and plasmid pBR322 that were generated in a recA derivative of Escherichia coli are described. Each resulted from two illegitimate recombination events that resulted in the substitution of part of the lambda genome by part of the plasmid genome. The nucleotide sequences at the six lambda-plasmid junctions were determined and compared with the sequences of the lambda and plasmid genomes before recombination. Each recombination occurred at a short region of homology in the two genomes, and other short regions of homology were found near some of the junctions. The structures of these junctions are similar to those resulting from illegitimate recombination in animal cells. A model to explain how these multiple illegitimate recombination events could result from a cascade of DNA gyrase-catalyzed recombinations is discussed.
Subject(s)
DNA, Viral/analysis , Recombination, Genetic , Bacteriophage lambda , Base Sequence , DNA Topoisomerases, Type II/metabolism , DNA Transposable Elements , PlasmidsABSTRACT
The nucleotide sequences involved in the illegitimate recombination of four recombinants between bacteriophage lambda DNA and pBR322 in E. coli (lambda TA6, lambda KA3, lambda TA1R, and lambda KA7) were determined. Each resulted from recombination between regions of homology of 10 to 13 base pairs. The presence of a recA+ allele was found to stimulate recombination between lambda DNA and pBR322 approximately 10-fold. Lambda TA6, lambda KA3, and lambda KA7 were isolated in the presence of a recA+ allele and therefore, may have been generated by the recA recombination system. However, lambda TA1R was isolated in a recA mutant, and was presumably generated by a different recombination system. The possibility that it was generated by DNA gyrase is discussed. Two recombination events were required to form lambda KA7, which may indicate that it also was generated by DNA gyrase.
