Four genes encode acetylcholinesterases in the nematodes Caenorhabditis elegans and Caenorhabditis briggsae. cDNA sequences, Genomic structures, mutations and in vivo expression

We report the full coding sequences and the genomic organization of the fou r genes encoding acetylcholinesterase (AChE) in Caenorhabditis elegans and Caenorhabditis briggsae, in relation to the properties of the encoded enzym es. ace-1 and ace-2, located on chromosome X and I, respectively, encode tw o AChEs (ACE-1 and ACE-2) that present 35% identity. The C-terminal end of ACE-1 is homologous to the C terminus of T subunits of vertebrate AChEs. AC E-1 oligomerizes into amphiphilic tetramers. ACE-2 has a hydrophobic C term inus of H type. It associates into glycolipid-anchored dimers. In C. elegan s and C. briggsae, ace-3 and ace-4 are organized in tandem on chromosome II , with only 356 nt and 369 nt, respectively, between the stop codon of ace- 4 (upstream gene) and the ATG of ace-3. ace-3 produces only 5 % of the tota l AChE activity. It encodes an H subunit that associates into dimers of gly colipid-anchored catalytic subunits, which are highly resistant to the usua l AChE inhibitors, and which hydrolyze butyrylthiocholine faster than acety lthiocholine. ACE-4 is closer to ACE-3 (54 % identity) than to ACE-1 or ACE -2. The usual sequence FGESAG surrounding the active serine residue in chol inesterases is changed to FGQSAG in ace-4. ACE-4 was not detected by our cu rrent biochemical methods, although the gene is transcribed in vivo. Howeve r the level of ace-4 mRNAs is far lower than those of ace-1, ace-2 and ace- 3. The ace-2, ace-3 and ace-4 transcripts were found to be trans-spliced by both SL1 and SL2, although these genes are not included in typical operons . The molecular bases of null mutations g72 (ace-2), p1304 and dc2 (ace-3) have been identified. (C) 2000 Academic Press.