An Escherichia coli recBCsbcBrecF host permits the deletion-resistant propagation of plasmid clones containing the 5'-terminal palindrome of minute virus of mice.

The deletion events that have plagued attempts to maintain molecular clones with long palindromic DNA sequences in Escherichia coli have been shown to be less frequent in recBCsbcB hosts [Collins et al., Gene 19 (1982) 139-146]. This study sought to determine if such hosts would permit the stable propagation of plasmid clones carrying the deletion-generating, 206 nucleotide (nt) long, imperfect palindrome derived from the 5' terminus of the genome of minute virus of mice (MVM), an autonomous parvovirus [Astell et al., Nucleic Acids Res. 11 (1983) 999-1018]. To this end these hybrid plasmids were used to transform several different mutant recBCsbcB hosts, followed by the isolation and restriction mapping of plasmid DNA from selected transformants. Characterization of plasmid DNA isolated from a recBCsbcBrecF host indicated deletion-resistant propagation of the intact species. Sequence analysis of unamplified and chloramphenicol (Cm)-amplified plasmid DNA obtained from these clones confirmed the integrity of the palindromic region of the viral DNA insert.