The stimulation of recombination in partial diploids of Escherichia coli K12 by ultraviolet light and mutagenic chemicals

E. coli K12 F-prime cells that are diploid for the histidine operon were used in a study of recombination between the episome and the chromosome. The partial diploids had a C[raised -] allele in the exogenote and an I[raised -] allele in the endogenote. The frequency of total homogenote formation was enhanced with the various recombinogenic agents such as MNNG, DES, MMS, and ultraviolet light. The ratios of C[raised -] to I[raised -] homogenotes were also increased. This indicates a preference for the minus allele that is in the exogenote in such a non-reciprocal recombinational event. The nature of the minus allele in the exogenote may have had some slight effect on the frequency of total homogenote formation. The strains tested fell into one of two groups according to the frequency of spontaneous homogenotes. One group was low (0.26% to 0.39%), and the other was higher (0.61% to 0.71%). Different alleles may also affect the ratio of C[raised -] to I[raised -] homogenotes. A rec A[raised -] strain produced few detectable homogenotes as would be expected in a recombination deficient strain. The rec A[raised -] strain was low in induced auxotrophs and high in F[raised -] haploid formation. The hcr[raised -] mutation caused a 10 to 20-fold increase in UV sensitivity. The UV induced homogenote formation in this strain occurred at a higher frequency than wild type. UV[raised s] markers introduced into strain 5059 caused the cells to be sensitive to UV light to different degrees. Spontaneous homogenote formation was either increased or decreased; but the ratio of C[raised -] to I[raised -] homogenotes was similar to wild type 5059. The induced formation of C[raised -] to I[raised -] homogenotes varied between the different recombinogenic agents used and between different strains. One strain appeared to be some kind of rec[raised -] mutant.