1. UV radiation mutagenesis in C. elegans: Helen Stewart and David Baillie have noted that many UV radiation-induced mutations are chromosomal rearrangements rather than point mutations. We have begun to extend this observation by isolating UV radiation-induced mutations in
fem-3 and
unc-22. As suggested to us by Judith Kimble, and as will be described at the meeting,
fem-3 is particularly well suited for these studies. Mutations have been selected at low and high radiation fluences, as well as in both rad(+) and rad(-) genetic backgrounds. These are currently the subject of both genetic and molecular analyses, with the ultimate hope of elucidating specific sequence contexts which are misrepaired into deficiencies. 2. Cloning a rad gene: We have isolated two allelic mutations in the high-hopper strain TR679 which confer hypersensitivity to methyl methanesulfonate and UV radiation. They map in between
unc-36 and
dpy-17 on linkage group III. Each mutation was crossed 12 times into an N2 background, several of which including forced recombinations in between the mutations and either
unc-36 or
dpy-17. Southern blots were performed, using Tcl as a probe (kindly provided by Phil Anderson) and revealed one novel Tc l- containing fragment in one mutant and three in the other. We are currently cloning these. Since both mutants are hypersensitive only during embryogenesis, we look forward to performing Northern blot analyses in order to determine if this developmental regulation of DNA is exercised at the transcriptional level. 3. The rad mutants are not hypersensitive to 8-methoxypsoralen (8MOP) phototreatment. Extending the observations of Fujita and coworkers (Photochem. Photobiol. 39, 831), survival of three staged populations N2 and four rad mutants was determined after 8-MOP phototreatment. As opposed to their responses after exposure to other DNA-damaging agents, none of the four were hypersensitive. Split-dose experiments indicated that DNA-DNA crosslinks were primarily responsible for lethality. Little if any crosslink repair was observed in N2 using two different assays, explaining why the rad mutants were not hypersensitive to 8-MOP inactivation.