We have been studying
sel-8 , a suppressor of
lin-12(d) mutations that also shows genetic interactions with
glp-1 (1). The one existing
sel-8 allele,
sa54 , suppresses
lin-12(d) in an allele-nonspecific and dose-dependent way. In an otherwise wild-type background,
sel-8(
sa54) causes an incompletely penetrant early embryonic lethality at 15C. The lethality can be partially rescued by zygotic
sel-8 activity. We used three-factor mapping to locate
sel-8 in an interval of LG III between
ben-1 and
unc-93 that contains seven predicted ORFs. We sequenced these ORFs from a
sel-8(
sa54) mutant, and found a nonsense mutation in one ORF, C32A3.1. Over 95% of the other ORFs in this region have been sequenced and no other mutations have been found. The nonsense mutation cosegregates with the
sel-8 suppression and cold-sensitive embryonic lethality phenotypes. In addition, RNAi using dsRNA from C32A3.1 produces embryonic lethality in 95% of F1s in an N2 background. Surviving F1s show defects characteristic of loss of
lin-12 activity as well as germline proliferation defects reminiscent of loss of
glp-1 activity. Based on the RNAi phenotype and on the presence a single nonsense mutation in
sel-8(
sa54) animals, we conclude that C32A3.1 is
sel-8 . C32A3.1 is predicted to encode a glutamine-rich 468 amino acid protein with no similarity to any proteins in the database. It does not appear to contain a signal sequence or transmembrane domains. The nonsense mutation occurs relatively late in the sequence and this observation in combination with the RNAi data suggests that
sel-8(
sa54) is probably not a null allele. We are in the progress of analyzing
sel-8 further genetically and molecularly, and we will report on our progress at the meeting. 1. Tax, F.E., J.H. Thomas, E.L. Ferguson, and H.R. Horvitz, Genetics 147:1675-1695 (1997).