Mutation in the
unc-17 region of the
cha-1 or choline levels, but causes abnormal accumulation of acetylcholine (ACh)(1). To further clarify the related genes, we isolated spontaneous mutants resistant to trichlorfon using mutator strains. Of twenty resistants, five mutations were assigned to the
unc-13(
cn490), 355), 347), 146) and
unc-10(
cn257) genes. Another mutation,
cn252 was 2.5% distant to the right from dpy- 11(V) but complements near by the gene
unc-42 allele
e270. The mutation was therefore tentatively denoted as
tcf-1. In addition to resistance to acetylcholinesterase inhibitors, all mutants exhibited abnormal movement. These mutations are classified into two groups based on ACh levels: those with normal ACh levels (
unc-10 and
unc-13 mutations) and those with abnormally high ACh levels (
unc-13, d
unc-18 mutations). Mutations in the latter gene groups also exhibited growth retardation and small body size in adulthood. We are especially interested in the latter group for elucidating mechanism of synaptic transmission of ACh. Three mutations,
unc-13(
cn490),
tcf-1(
cn252) and
unc-18(
cn347) frequently reverted to wild-type phenotype, indicating mutations were induced by insertion of Tc1. Of the isolates, the
unc-18(
cn347) mutation showed the most severely paralyzed phenotype and the highest ACh levels. No double mutants were detected between
unc-17(
e245) and
unc-18(
cn347), suggesting the important contribution to the survival. Southern blotting of the BglII restriction digestion revealed one extra band 6.8 kb, unique to the
unc-18(
cn347) mutant DNA. Cloning of this fragment is currently in progress. We thank Drs. P. Anderson, B. Waterston, D. Moerman and Miss I. Mori for giving us mutator strains and valuable advice. We want to thank Drs. A. Levitt and S. Emmons for giving us Tc1. We are also grateful to Dr. J. Rand for information on other trichlorfon resistant genes that were already mapped as Unc mutants.