The KGB-1 MAPK cascade, consisting of MLK-1 (MLK-type MAPKKK), MEK-1 (MKK7-type MAPKK) and KGB-1 (JNK-type MAPK), regulates heavy metal stress response and fertility in Caenorhabditis elegans . To identify downstream components in the KGB-1 pathway, we isolated KGB-1-binding proteins using yeast two-hybrid method. 36 different genes were isolated and one of them encodes FOS-1 (corresponding to F29G9.4) homologous to mammalian transcription factor Fos. In order to analyze the function of FOS-1, the
fos-1(
km30) deletion mutant was isolated by TMP/UV method.
fos-1(
km30) deletes most of the bZIP domain in FOS-1, suggesting that
km30 is presumably a null allele. The
fos-1(
km30) deletion mutant showed a sterile phenotype characterized by the absence of mature oocytes. Similar phenotype was observed in
kgb-1 null mutants at high temperature. Although
kgb-1 mutants show hypersensitivity to heavy metal ions, the
fos-1(
km30) mutation had no effect on the sensitivity to heavy metals. These results suggest that FOS-1 regulates fertility in the KGB-1 MAPK pathway.