Multiple mutations induced in Bacillus subtilis by ultraviolet light

Genetic and molecular analyses of UV radiation-induced mutations in the fem-3 gene of Caenorhabditis elegans

The utility of a new target gene (fem-3) is described for investigating the molecular nature of mutagenesis in the nematode Caenorhabditis elegans. As a principal attribute, this system allows for the selection, maintenance and molecular analysis of any type of mutation that disrupts the gene, including deletions. In this study, 86 mutant strains were isolated, of which 79 proved to have mutations in fem-3. Twenty of these originally tested as homozygous inviable. Homozygous inviability was expected, as Stewart and coworkers had previously observed that, unlike in other organisms, most UV radiation-induced mutations in C. elegans are chromosomal rearrangements of deficiencies (Mutat. Res. 249, 37-54, 1991). However, additional data, including Southern blot analyses on 48 of the strains, indicated that most of the UV radiation-induced fem-3 mutations were not deficiencies, as originally inferred from their homozygous inviability. Instead, the lethals were most likely "coincident mutations" in linked, essential genes that were concomitantly induced. As such, they were lost owing to genetic recombination during stock maintenance. As in mammalian cells, yeast and bacteria, the frequency of coincident mutations was much higher than would be predicted by chance.

Double mutations induced in Escherichia coli by ultraviolet light

Double mutations to azide resistance and to bacteriophage T5 resistance of genes separated by more than 50 kilobases were induced in Escherichia coli WP2s in chemostat cultures by exposure to a single low dose of ultraviolet light. Frequencies of induced double mutations were three orders of magnitude greater than would be predicted by chance. Reversions from azide resistance and phage resistance occurred independently, showing that that the double mutation was not due to pleiotropic effects of a single gene mutation. These results support earlier findings which show that low doses of ultraviolet light induce multiple gene mutations in Bacillus subtilis over a similarly broad range.