Recovery of Recombination Deficient Mutants of Escherichia coli K-12 from Ultraviolet Irradiation

Although the recombination deficient, or rec mutants of Escher ichia coli K-12 are more sensitive to ultraviolet light (UV) than their ree + counter-parts (Clark and Margulics, 1965; Howard-Flanders and Theriot, 1966; Van de Putte et al. 1966), some of them appear to have acquired two recovery processes not observed in wild-type K-12. Similar processes were originally described in E. coli B irradiated with UV. The first, called liquid holding recovery, or LHR (Castellani, Jagger, and Setlow, 1964; Harm, 1966; Jagger, 1964; Jagger, Wise, and Stafford, 1964), is characterized by an increase in the proportion of colony-forming units when irradiated cells arc held in the dark in buffer and plated at intervals on a complex medium such as nutrient agar or yeast extract (Charles and