The human La protein was first described as an autoantigen present in the sera of systemic lupus erythematosus (SLE) and Sjogren's patients. Since then, a large family of La-related proteins has been described (Wolin & Cedervall, 2002). La family members are all characterized by a highly conserved La Motif (LaM), which has RNA-binding activity. Typically, LaM family members, including human La and yeast Lhp1p, harbor additional RNA Recognition Motifs (RRMs) and localize predominately to the nucleus. Both La and Lhp1p bind RNA polymerase III transcripts (i.e. tRNAs, 5S rRNAs and snRNAs) and direct their maturation. In contrast, two atypical yeast LaM proteins, Sro9p and Slf1p, do not have any other recognizable RNA-binding domains and are predominately cytoplasmic. Sro9p and Slf1p are believed to play a role in mRNA metabolism, although it is unclear what their RNA targets and exact mechanism of control might be (Sobel and Wolin, 1999). The Caenorhabditis elegans genome encodes three LaM family members: C44E4.4, T12F5.5 and R144.7/larp-1. Of the three, LARP-1 is most closely related to yeast Sro9p and Slf1p. Initial RNAi experiments indicated that LARP-1 might be important for oogenesis. To confirm the RNAi results, we isolated
larp-1(
q783), a deletion mutant that eliminates expression of LARP-1 protein. We find that
larp-1(
q783) hermaphrodites are self-fertile, but have more developing oocytes in the proximal gonad than normal. We have also found active MAP kinase to be more abundant in
larp-1(
q783) germ lines than in wild-type. Our working model is that LARP-1 negatively regulates MAPK activity to ensure proper oogenesis.