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, an 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 recently to play important roles in the innate immune response. Previous screens for recessive suppressors of the mutant phenotype of
unc-93(
e1500sd) animals were not designed to identify suppressors that cause lethality. To seek essential genes that 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 is a partial suppressor and causes sterility or carries a closely linked mutation that causes sterility.
n4564 and
n4588 are strong recessive suppressors and cause temperature-sensitive (ts) lethality or carry closely linked ts-lethal mutations. We found that
n4588 is a missense mutation in the gene
uaf-1, which encodes a worm homolog of the splicing factor U2AF65 (U2 snRNP auxiliary factor large subunit).
n4562 is a nonsense mutation in the gene Y116A8C.32, which encodes a worm homolog of the splicing factor SF1. U2AF65 and SF1 have been shown to interact with each other to regulate pre-mRNA splicing. Finally, we have identified a missense mutation in the gene
sig-7 in
n4564 mutant animals.
sig-7 encodes a highly conserved protein with a peptidyl-prolyl isomerase domain, an RRM (RNA recognition motif) and an RS (arginine/serine) rich domain. We found that
uaf-1(
n4588)
unc-93(
e1500) animals have an alternatively spliced
unc-93 transcript that encodes a truncated UNC-93 protein. This transcript is probably caused by the generation of a cryptic splice acceptor by the
unc-93(
e1500) mutation so that this new splice acceptor, instead of the endogenous splice acceptor, is recognized by the splicing machinery. We hypothesize that
n4588,
n4562 and
n4564 suppress
unc-93(
e1500) by affecting pre-mRNA splicing of the
unc-93 transcript. These results suggest that
unc-93(
e1500) can be used as a genetic system for the study of splice-site selection in vivo.