We have previously described mutants with muscle activation defective (Mac-d) or hyper-activated muscle (Mac-h) phenotypes. Mac genes were proposed to encode ion channels or other regulators of cell excitability. Mutants for a third class of genes are Mac-d in some tissues and Mac-h in others (Mac-m; muscle activation mixed). Perhaps Mac-m genes encode regulatory proteins that act on different effectors in different tissues (1). Animals with gain-of-function mutations in
unc-43 (
unc-43(gf)) are Mac-d in the egg-laying and enteric muscles and Mac-h in the body-wall muscles. Loss-of-function mutations (
unc-43(lf)) confer the reciprocal muscle phenotypes.
unc-43 appears to function widely in the nervous system, since
unc-43 mutations also confer defects in functions other than muscle activation.
unc-43(gf) causes an abnormally long defecation cycle period, while
unc-43(lf) confers an inappropriate repeat or "echo" of the defecation motor program. We have shown that the previously described
dec-8(
sa200) mutation (2) is a partial loss-of-function allele of
unc-43.
unc-43(gf) causes sluggish locomotion, while
unc-43(lf) causes a "jumpy" phenotype, apparently consisting of rapid, sequential initiation and cessation of locomotion. Finally, we observed that
unc-43(gf) can promote dauer formation in combination with other Daf-c or syn-Daf (3) mutations (our observations; E. Malone, M. Ailion and J. Thomas, pers. comm.). We mapped
unc-43 to a small region between
daf-14 and
mec-3, which was recently sequenced by the C. elegans genome sequencing consortium. Using the candidate gene approach, we found that
unc-43 encodes a putative type II Ca++/calmodulin-dependent protein kinase (CaMKII). In other systems, CaMKII has been well-characterized biochemically but not genetically. We have sequenced eleven
unc-43 mutations, including an early stop mutation and a change of an aspartate that is universally conserved in serine/threonine kinases. These putative null mutations confer phenotypes comparable to most loss-of-function alleles. CaMKII is thought to function in short-term learning and memory, and to exist as a homododecamer that autophosphorylates upon activation by Ca++/calmodulin. The resulting activated kinase has relatively low specific activity, but can remain activated for hours, giving it the potential to provide a long-term molecular memory of Ca++ influx. Based on in vitro studies, CaMKII is thought to modulate ion channel function directly by phosphorylation. We have previously reported that loss-of-function mutations in
unc-103 suppress the
unc-43(gf) enteric muscle defect, but not other defects.
unc-103 is closely related to the human erg K+ channel, which is defective in some individuals with the hereditary cardiac arrhythmia disorder Long QT Syndrome (4). We have also found that mutations in the
tax-4 cyclic-nucleotide gated cation channel (5) suppress the Mac-h body-wall muscle defect conferred by
unc-43(gf). We speculate that
unc-43 regulates the function of the
unc-103 and
tax-4 gene products by directly phosphorylating the channels, and tests of this are in progress. (1) Reiner, Weinshenker and Thomas (1995) Genetics 141: 961-976. (2) Liu and Thomas (1994) J. Neurosci. 14: 1953-1962. (3) Thomas, Iwasaki, Malone and Ailion (1995) WBG 13(5): 45. (4) Reiner, Nishiwaki, Miwa, Levitan and Thomas (1996)WCWM Abstract 129. (5) Komatsu, Mori and Ohshima (1995) IWM abstract 318.