The development of the Caenorhabditis elegans vulva requires the activity of the Ras signaling pathway. To identify components of this pathway, we screened for mutations that suppress the multivulval phenotype caused by
let-60(
n1046gf) , a mutation that constitutively activates Ras. Forty-three alleles comprising 20 complementation groups were identified. These genes include conserved members of the Ras signaling cascade, such as Raf (
lin-45), KSR (
ksr-1), MEK (
mek-2), MAPK (
mpk-1) and an ETS transcription factor (
lin-1). One of these alleles,
n2508 , defines a new complementation group. The
n2508 mutation strongly suppressed the
let-60(
n1046) multivulval phenotype, but did not suppress the
lin-1(
n383) multivulval phenotype, suggesting that the affected gene may act downstream of
let-60 but upstream of the transcription factor
lin-1 . In a wild-type genetic background, the
n2508 mutation did not dramatically affect vulval development, but
n2508 did cause a partially penetrant larval lethality. The
n2508 lethal phenotype was enhanced by loss-of-function mutations in
let-60 ras and
sur-8 , indicating that the gene affected by
n2508 functions in other Ras-mediated processes such as excretory duct cell development. We used single nucleotide polymorphisms in the C. elegans strain, RC301, to map the
n2508 mutation to
a11.2kb region on chromosome II that encompasses regions of three predicted genes. Transgenic animals were constructed expressing wild-type fragments of genomic DNA from within this region. One gene was identified that was capable of restoring the multivulval phenotype in the
n2508;
n1046 strain. The identified gene encodes a protein that is similar to a human tumor suppressor protein. Interestingly, RNA inhibition of the
n2508 gene increases the penetrance of the multivulval phenotype in both the
n1046 and the
n2508;
n1046 strains, suggesting that this gene product exerts a negative regulatory influence upon Ras signaling in C. elegans .