CHARACTERIZATION OF A NULL MUTATION IN ACE-1, THE GENE ENCODING CLASS-A ACETYLCHOLINESTERASE IN THE NEMATODE CAENORHABDITIS-ELEGANS

Two genes (ace-1 and ace-2) encode two major classes (A and B) of acetylcholinesterase (AChE) in the nematode Caenorhabditis elegans. A null mutation in ace-1 (allele p1000) suppresses all acetylcholinesterase activity of class A. We have identified an opal mutation TGG (W99) --> TGA (Stop) as the only alteration in the mutated gene. This leads to a truncated protein (98 instead of 620 amino acids) with no enzymatic activity, The mutation also reduces the level of ace-1 transcripts to only 10% of that in wild-type animals. This most likely results from a destabilization of mRNA containing the nonsense message. In contrast, compensation of class B by class A AChE in the null mutant strain ace-2 takes place with unchanged ace-1 mRNA level and enzymatic activity similar to class A AChE.