A novel assay for illegitimate recombination in Escherichia coli: Stimulation of λ bio transducing phage formation by ultra-violet light and its independence from RecA function

Abstract

We developed a novel assay system for illegitimate recombination, in which the frequency of the formation of λ Spi − phages formed during prophage induction was measured with an E. coli P2 lysogen as the indicator bacteria. Since almost all of the λ Spi − phages thus detected contain attR, they have essentially the same structures as λ bio transducing phages, indicating that this assay system enables us to detect specialized transducing phages that produce heterogenote transductants, thus ignoring the occurrences of docL and docR particles which carry only one cohesive end. The following results on the formation of specialized transducing phages have been obtained by this assay system to date. (1) Irradiation with UV light greatly enhanced the formation of λ Spi − phages. (2) Treatments with other DNA-damaging agents also enhanced the formation of λ Spi − phages. (3) Illegitimate recombination during prophage induction does not require the RecA function, indicating that enhancement of λ Spi − phage formation is not controlled by the SOS regulatory system. (4) Preliminary results suggested that DNA gyrase is involved in the formation of λ Spi − phage during prophage induction. Since the above results were consistent with most of the previous observations on the illegitimate recombination in other systems, the Spi − assay system can provide important clues to the mechanism of illegitimate recombination.