Instability of repeated DNAs during transformation in Escherichia coli

Vera I. Hashem, Elzbieta A. Klysik, William A. Rosche, Richard R. Sinden

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


Escherichia coli has provided an important model system for understanding the molecular basis for genetic instabilities associated with repeated DNA. Changes in triplet repeat length during growth following transformation in E. coli have been used as a measure of repeat instability. However, very little is known about the molecular and biological changes that may occur on transformation. Since only a small proportion of viable cells become competent, uncertainty exists regarding the nature of these transformed cells. To establish whether the process of transformation can be inherently mutagenic for certain DNA sequences, we used a genetic assay in E. coli to compare the frequency of genetic instabilities associated with transformation with those occurring in plasmid maintained in E. coli. Our results indicate that, for certain DNA sequences, bacterial transformation can be highly mutagenic. The deletion frequency of a 106bp perfect inverted repeat is increased by as much as a factor of 2×105 following transformation. The high frequency of instability was not observed when cells stably harboring plasmid were rendered competent. Thus, the process of transformation was required to observe the instability. Instabilities of (CAG)·(CTG) repeats are also dramatically elevated upon transformation. The magnitude of the instability is dependent on the nature and length of the repeat. Differences in the methylation status of plasmid used for transformation and the methylation and restriction/modification systems present in the bacterial strain used must also be considered in repeat instability measurements. Moreover, different E. coli genetic backgrounds show different levels of instability during transformation.

Original languageEnglish (US)
Pages (from-to)39-46
Number of pages8
JournalMutation Research - Fundamental and Molecular Mechanisms of Mutagenesis
Issue number1-2
StatePublished - May 22 2002


  • Inverted repeat
  • Repeat instability
  • Spontaneous mutation
  • Triplet repeats

ASJC Scopus subject areas

  • Molecular Biology
  • Genetics
  • Health, Toxicology and Mutagenesis


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