Characterization of revertants of unc-93(e1500) in Caenorhabditis elegans induced by N-ethyl-N-nitrosourea.

Phenotypic reversion of the rubber-band, muscle-defective phenotype conferred by unc-93(e1500) was used to determine the utility of N-ethyl-N-nitrosourea (ENU) as a mutagen for genetic research in Caenorhabditis elegans. In this system, ENU produces revertants at a frequency of 3 x 10(-4), equivalent to that of the commonly used mutagen, EMS. The gene identity of 154 ENU-induced revertants shows that the distribution of alleles between three possible suppressor genes differs from induced by EMS. A higher percentage of revertants are alleles of unc-93 and many fewer are alleles of sup-9 and sup-10. Three revertants complement the three known suppressor genes; they may therefore identify a new gene product(s) involved in this system of excitation-contraction coupling in C. elegans. Molecular characterization of putative unc-93 null alleles reveals that the base changes induced by ENU are quite different from those induced by EMS; specifically we see an increased frequency of A/T-->G/C transitions. The frequency of ENU-induced intragenic deletions is found to be 13%. We suggest that ENU, at concentrations below 5 mM, will be a superior mutagen for studies of protein function in C. elegans.