Worm Breeder's Gazette 13(5): 37 (February 1, 1995)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

A genomic fragment containing a C. elegans homolog of cyclic nucleotide-gated channel rescued a tax-4 mutation

Hidetoshi Komatsu, Ikue Mori and Yasumi Ohshima

Department of Biology, Faculty of Science, Kyushu University, Fukuoka 812,

tax-4 mutations cause animals to move almost randomly on a thermal
gradient and are coupled with chemotactic defects (Mori et. al. 1993, WBG
12(5):73, Bargmann et. al. 1993, Cell 74:515). We previously reported that
tax-4(ks11) maps to the region between lin-12 and emb-9 on the LGIII
(Komatsu et. al. 1994, WBG 13(3):67) that has already been completely
sequenced as part of the C. elegans genome project.

To clone tax-4, we tested the ability of cosmids spanning between lin-12
and emb-9 to rescue the tax-4 mutant phenotype. Both F54G8 and R07A8
cosmids were found to rescue the thermo- and chemotactic defects. By
testing various subclones from the region common to those two cosmids, we
identified a 6.0 kb region that rescued the thermotactic defect of a tax-4

Based on the information of genomic sequence (thanks to ACEDB), this
region could encode only one gene, a C. elegans homolog of the cyclic
nucleotide-gated (CNG) cation channel which is an essential component of
olfactory and visual signal transductions in mammals. The C. elegans CNG
channel is homologous to the bovine cGMP-gated channel with 36.2% sequence
identity, to the human cGMP-gated channel with 35.9% sequence identity, to
the mouse cGMP-gated channel with 35.2% sequence identity, and to the rat
cAMP-gated channel with 33.5% sequence identity. The presumed cyclic
nucleotide binding site in the carboxyl terminus region is highly
homologous to those of mammalian CNG channels with over 70% sequence
identity. The C. elegans CNG channel predicted from the genomic sequence
has however distinct characteristics; this CNG channel is 772 amino acids
in length as compared with other mammalian channels which are about 650
amino acids in length, and there is little homology in the amino terminus
region, which is thought to form the first transmembrane domain and has
been recently reported to bind to calcium-calmodulin in mammals (Liu et.
al. 1994, Science 266:1348-1354). We are analyzing the cDNAs of the wild
type and tax-4 mutants to establish the encoded amino acids and that tax-4
encodes the CNG channel homolog.

If tax-4 encodes a cyclic nucleotide-gated channel, our results may
provide an important implication; a cyclic nucleotide-gated channel plays
a significant role either in a thermosensory signal transduction or in the
integration of different sensory signal transductions.