radE, a new radiation - sensitive locus in Dictyostelium discoideum

Dictyostelium discoideum strain M28 was found to carry a radiation-sensitive mutation. This allele, rad-100, was recessive in heterozygous diploids and mapped in linkage group III. Complementation analysis and survival studies on strains carrying rad-100 suggested that this allele defines a new radiation-sensitive locus, radE, in D. discoideum. radE strains were moderately sensitive to ultraviolet light and slightly sensitive to 137Cs gamma rays. radE strains also exhibited increased sensitivity to killing by N-methyl-N'-nitro-N-nitrosoguanidine but not by ethyl or methyl methylsulphonate. The frequency of spontaneous methanol-resistant (acrA) mutants was approximately the same in cultures of radE and radE+ strains. However, when amoebae of these strains were irradiated with ultraviolet light, the frequency of induced mutants was significantly lower in cultures of the radE strain. Furthermore, when amoebae of wild-type strain NC4 were plated in the presence of caffeine after ultraviolet-irradiation, the survival curves were very similar to the curves obtained for amoebae of radE strains in the presence or in the absence of caffeine. These results suggested that the radE 100 mutation and caffeine interfered with an error-prone DNA repair pathway in D. discoideum. (author)