Phenotypes of Caenorhabditis elegans
unc-18 and
unc-64 gene mutations are similar. While
unc-18 is known to be essential for normal synaptic transmission (Hosono, R., Hekimi, S., Kamiya, Y., Sassa, T., Murakami, S., Nishiwaki, S., Miwa, J., Taketo, A., and Kodaira, K.-I. (1992) J. Neurochem. 58, 1517-1525), the function of
unc-64 remains unclear. Here we describe the cloning, and the molecular and genetic characterization of the
unc-64 gene, especially in relation to
unc-18.
unc-64 encodes a protein (C. elegans syntaxin) showing sequence and structural similarities to mammalian syntaxin 1A. From
unc-64, at least three types of poly(A)+ RNA are transcribed, which encode two types of syntaxin that differ in the deduced transmembrane domain. In gene expression,
unc-64 closely resembles
unc-18, that is, both are expressed in neural cells, especially in motor neurons and neurons constituting head ganglions. C. elegans syntaxin binds to UNC-18 with high affinity. The
unc-64 (
e246) mutation producing a mild phenotype causes an Ala-->Val conversion in the conserved COOH-terminal region in mammalian syntaxin 1A or Drosophila syntaxin-1A whose site is included in three types of transcripts. The binding of the mutant C. elegans syntaxin to UNC-18 is greatly reduced, indicating the mutation site contributes to the binding.