CHARACTERIZATION OF REVERTANTS OF UNC-93(E1500) IN CAENORHABDITIS-ELEGANS INDUCED BY N-ETHYL-N-NITROSOUREA

Phenotypic reversion of the rubber-hand, muscle-defective phenotype co nferred by unc-93(e1500) aas used to determine the utility of N-ethyl- N-nitrosourea (ENU) as a mutagen for genetic research in Caenorhabditi s 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 g ene identity of 154 ENU-induced revertants shows that the distribution of alleles between three possible suppressor genes differs from that induced by EMS. A higher percentage of revertants are alleles of unc-9 3 and many fewer are alleles of sup-9 and sup-10. Three revertants com plement the three known suppressor genes; they may therefore identify a new gene product(s) involved in this system of excitation-contractio n coupling in C. elegans. Molecular characterization of putative unc-9 3 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 int ragenic deletions is found to be 13%. We suggest that ENU, at concentr ations below 5 mM, will be a superior mutagen for studies of protein f unction in C. elegans.