Molecular and General Genetics MGG

, Volume 211, Issue 2, pp 320–325

Transposon Tn21 encodes a RecA-independent site-specific integration system


  • Eduardo Martinez
    • Departamento de Biologia MolecularUniversidad de Cantabria
  • Fernando de la Cruz
    • Departamento de Biologia MolecularUniversidad de Cantabria

DOI: 10.1007/BF00330610

Cite this article as:
Martinez, E. & de la Cruz, F. Mol Gen Genet (1988) 211: 320. doi:10.1007/BF00330610


The IncW plasmid R388 and the DNA region of Tn21 containing the Smr and the Sur genes are capable of RecA-independent recombination. This recombination occurs at a relatively high frequency (up to 10-4 recombinants per recipient molecule) and results in integration of the two plasmids. No detectable repeats are formed in the process. The crossover points have been confined to a 0.4-kb homologous segment in both plasmids which contains a 59-bp DNA sequence presumably involved in the acquisition of new genes by Tn21 and its relatives (Cameron et al. 1986). It is likely that the recombination occurs precisely at this point. At least one trans-acting function (an integrase) is required for the site-specific recombination. It has been localized to a 1456-bp BstEII-BamHI fragment of Tn21 and can efficiently complement the integration of plasmids containing the integration site.

Key words

Tn21 integraseSite-specific recombinationTransposon evolutionEscherichia coli
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© Springer-Verlag 1988