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 investigatin g the molecular nature of mutagenesis in the nematode Caenorhabditis e legans. As a principal attribute, this system allows for the selection , maintenance and molecular analysis of any type of mutation that disr upts the gene, including deletions. In this study, 86 mutant strains w ere isolated, of which 79 proved to have mutations in fem-3. Twenty of these originally tested as homozygous inviable. Homozygous inviabilit y 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. 24 9, 37-54, 1991). However, additional data, including Southern blot ana lyses on 48 of the strains, indicated that most of the UV radiation-in duced fem-3 mutations were not deficiencies, as originally inferred fr om their homozygous inviability. Instead, the lethals were most likely ''coincident mutations'' in linked, essential genes that were concomi tantly 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 pr edicted by chance.