Two functionally dependent acetylcholine subunits are encoded in a single Caenorhabditis elegans operon.
The deg-3 gene from the nematode Caenorhabditis elegans encodes an alpha subunit of a nicotinic acetylcholine receptor that was first identified by a dominant allele, u662, which produced neuronal degeneration. Because deg-3 cDNAs contain the SL2 trans-spliced leader, we suggested that deg-3 was transcribed as part of a C. elegans operon. Here we show that des-2, a gene in which mutations suppress deg-3(u662), is the upstream gene in that operon. The des-2 gene also encodes an alpha subunit of a nicotinic acetylcholine receptor. As expected for genes whose mRNAs are formed from a single transcript, both genes have similar expression patterns. This coexpression is functionally important because (i) des-2 is needed for the deg-3(u662) degenerations in vivo; (ii) an acetylcholine-gated channel is formed in Xenopus oocytes when both subunits are expressed but not when either is expressed alone; and (iii) channel activity, albeit apparently altered from that of the wild-type channel, results from the expression of a u662-type mutant subunit but, again, only when the wild-type DES-2 subunit is present. Thus, the operon structure appears to regulate the coordinate expression of two channel subunits.
Treinin
M
M
Department of Biological Sciences, Columbia University, New York, NY 10027, USA. millet_t@cc.huji.ac.il
Gillo
B
B
Liebman
L
L
Chalfie
M
M
D000109:Acetylcholine / Q000494:pharmacology*; D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics*; D005260:Female; D005786:Gene Expression Regulation; D017238:Genes, Helminth; D046911:Macromolecular Substances; D008564:Membrane Potentials / Q000187:drug effects; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D009876:Operon; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics; D011978:Receptors, Nicotinic / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D015183:Restriction Mapping; D016415:Sequence Alignment; D014158:Transcription, Genetic; D014982:Xenopus laevis
D046911:Macromolecular Substances; D012333:RNA, Messenger; D011978:Receptors, Nicotinic; D011993:Recombinant Fusion Proteins; D000109:Acetylcholine