Genetic stability and DNA rearrangements associated with a 2 x 1.1-Kb perfect palindrome in Escherichia coli.

We show that circular plasmids containing perfect palindromic regions of 2 x 1.1 kb can be propagated in sbcC strains of Escherichia coli, a result that is at variance with the well known observation that lambda DNA cannot tolerate palindromic regions larger than 2 x 265 bp. However, a significant fraction of these palindrome-containing plasmids can be recovered from E. coli strains either as linear molecules with hairpins at their ends or as head-to-head dimers, both in a RuvC-and RusA-independent manner. Our results suggests that large palindromes may form cruciforms in E. coli. However, palindrome-associated DNA rearrangements occur by a process that does not require any known cruciform resolvase activity. Our data support a replication-dependent model for the induction of DNA rearrangements by perfect palindromes.