Spectrum of spontaneous mutations in the cyclic AMP receptor protein gene on chromosomal DNA of Escherichia coli

We determined 46 spontaneous mutations occurring in the cyclic AMP receptor protein gene (crp) on the chromosomal DNA of Escherichia coli by the use of PCR cloning. Of 24 base substitutions, 17 were transversions and 7 transitions including all types of base substitutions. The frequency of the changes of A:T base pairs was similar to that of G:C pairs, suggesting that A:T pair is also a target for base substitution. Frameshifts including seven -1 and four +1 frameshifts occurred at the sites of a run of identical bases. Deletions extending 18 and 172 bases occurred at the sites where the deleted sequences were flanked by short repeated sequences at the junction. The insertions of IS2 element or its inverted sequence were detected in two and six mutations, respectively. The assay system of the mutation used here is available for the determination of the mutational spectrum of base substitutions.