Toward molecular cloning of
tax-4, a gene necessary for both thermo- and chemotactic responses of C. elegans Hidetoshi Komatsu, Ikue Mori and Yasumi Ohshima, Department of Biology, Faculty of Science, Kyushu University, Fukuoka 812, Japan Athermotactic mutations, which cause animals to move almost randomly on a thermal gradient, are always coupled with chemotactic defects(1). These mutations so far fall into 4 complementation groups, one of which defines
tax4 gene (
p678, ksl l,
ks28). All 3
tax4 mutants are athermotactic and defective in chemotaxis to NaCl, and at least one mutation,
p678, was recently found to cause abnormal responses to volatile odorants(2). These
tax4 mutants, however, seem to be normal for osmotic avoidance response and dye-fillings of amphid sensory neurons. To investigate the molecular bases underlying these multiple taxis defects, we have begun to clone
tax4 . First,
tax4 (ksl l ) was mapped to linkage group III. Further 3-factor crosses demonstrated that
taz4 (ksl l ) lay between
unc-32 and
unc-69. At that point, we anempted to rescue the
tax4 mutant using 40 50 cosmids covering the whole
unc-32 -
unc-69 interval. However, this strategy was unsuccessful: we failed to identify any cosmid, which could rescue
tax4 mutant phenotype. We then decided to genetically map the locus more precisely. A genetic mapping based on polymorphic Tcl sites(3) showed that
tox4 (ksl l ) maps to the region left of slP127 and to the right of mgP21 . The following 3-factor crosses indicated that
tax4 maps to the region between
unc-32 and
emb-9, and possibly near or right of
lin-12. From
tax4 (ksl l )/unc-32
emb-9 hermaphrodites, 9/16 Unc non-Emb recombinant progeny segregated
tax4. From
tax4 (ksl l )/
unc-32 lin-12 hermaphrodites, 2/2 Unc non-Lin recombinant progeny segregated
tax4. From
tax4 (ksl l )/dpy-l 9 eP6 eP7
unc-50 hermaphrodites, 1/11 Dpy non-Unc recombinant progeny segregated
tax4. While we are in the process of re-starting injection experiments using cosmids and YACs, we still want to narrow down the taJc4 region as much as possible using RFLPs and visible markers. We are aware of the fact that some types of genes are not able to be cloned easily by rescue experiments. (1) Mori et. al. (1993), WBG 12(5):73, (2) Bargmann et. al. (1993), Cell 74:515, (3) Williams et.al. (1992). Genetics 131:609