sup-9,
sup-10 and
unc-93 encode components of a presumptive C. elegans two-pore domain K+ channel complex. Rare gain-of-function mutants of each of these three genes have abnormal body muscle contraction and exhibit the rubberband phenotype: when prodded on the head, the animal contracts and relaxes along its entire body without moving backwards. Loss-of-function mutants of each of these genes have no obviously abnormal phenotype. The SUP-9 protein is similar to the mammalian Two-pore Acid Sensitive K+ channels TASK-1 and TASK-3.
sup-10 encodes a novel single transmembrane protein.
unc-93 encodes a multiple transmembrane protein that defines a novel family of proteins conserved from C. elegans to mammals. A mammalian UNC-93 homolog, UNC-93b, has been shown to play important roles in the innate immune response. To seek essential genes that might interact with
unc-93, we screened ~10,000 EMS-mutagenized F1
unc-93(
e1500sd) animals clonally for progeny with improved locomotion and identified three new suppressors,
n4562,
n4564 and
n4588.
n4588 and
n4564 cause recessive lethality at 25 degC, while
n4562 causes recessive sterility at all temperatures.
n4588 is a missense mutation in the gene
uaf-1, which encodes a C. elegans homolog of the splicing factor U2AF65 (U2 snRNP auxiliary factor large subunit).
n4562 is a nonsense mutation in the gene
sfa-1, which encodes a C. elegans homolog of the splicing factor SF1. We found that
uaf-1(
n4588)
unc-93(
e1500) animals have an abnormally spliced
unc-93 transcript that encodes a truncated loss-of-function UNC-93 protein. This transcript is caused by the generation of a cryptic 3' splice site by the
e1500 missense mutation, so that this new 3' splice site, instead of the endogenous 3' splice site, is recognized. However,
sfa-1(
n4562) does not cause abnormal splicing of the
unc-93(
e1500) transcript at the cryptic 3' splice site. We think that abnormal splicing of
unc-93 is not the reason that
uaf-1 and
sfa-1 mutations suppress
unc-93(
e1500). We have identified two missense mutations in the gene F43G9.10 in
n4564 mutant animals. F43G9.10 encodes a highly conserved nuclear protein of unknown function.
uaf-1 and F43G9.10 interact genetically, and F43G9.10 requires
uaf-1 to suppress
unc-93(
e1500). We hypothesize that
uaf-1(
n4588),
sfa-1(
n4562) and F43G9.10
(n4564) all suppress
unc-93(
e1500) by affecting the splicing of one or more unidentified genes required for
unc-93 activity.