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J Neurosci. 1999 Jul 1;19(13):5348-59.

The Caenorhabditis elegans unc-49 locus encodes multiple subunits of a heteromultimeric GABA receptor.

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  • 1Department of Biology, University of Utah, Salt Lake City, Utah 84112, USA.


Ionotropic GABA receptors generally require the products of three subunit genes. By contrast, the GABA receptor needed for locomotion in Caenorhabditis elegans requires only the unc-49 gene. We cloned unc-49 and demonstrated that it possesses an unusual overlapping gene structure. unc-49 contains a single copy of a GABA receptor N terminus, followed by three tandem copies of a GABA receptor C terminus. Using a single promoter, unc-49 generates three distinct GABAA receptor-like subunits by splicing the N terminus to each of the three C-terminal repeats. This organization suggests that the three UNC-49 subunits (UNC-49A, UNC-49B, and UNC-49C) are coordinately rescued and therefore might coassemble to form a heteromultimeric GABA receptor. Surprisingly, only UNC-49B and UNC-49C are expressed at high levels, whereas UNC-49A expression is barely detectable. Green fluorescent protein-tagged UNC-49B and UNC-49C subunits are coexpressed in muscle cells and are colocalized to synaptic regions. UNC-49B and UNC-49C also coassemble efficiently in Xenopus oocytes and HEK-293 cells to form a heteromeric GABA receptor. Together these data argue that UNC-49B and UNC-49C coassemble at the C. elegans neuromuscular junction. Thus, C. elegans is able to encode a heteromeric GABA receptor with a single locus.

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