P granules are distinctive organelles that are observed in the cytoplasm of all germline cells, except sperm, throughout the life cycle of C. elegans. We have identified a protein component of P granules, PGL-1. By antibody staining, PGL-1 is associated with P granules at all stages of development and therefore is a constitutive component of P granules. PGL-1 is a novel protein, which contains an RGG box (a series of arg-gly-gly repeats) at its carboxy terminus. RGG boxes are seen in many RNA-binding proteins, including fibrillarins, nucleolins, hnRNP proteins, and RNA helicases such as Drosophila Vasa. Thus, PGL-1 is predicted to be an RNA-binding protein. Null mutations in
pgl-1 result in defective P granules, which lack several P-granule epitopes. Probably as a consequence of P-granule defects,
pgl-1 mutants are sterile, with both a maternal and a zygotic component to the sterility. About 40% of
pgl-1/pgl-1 progeny (F1) of
pgl-1/+ mothers are sterile, apparently as a result of formation of defective gametes. The F1
pgl-1/pgl-1 worms that are fertile produce many dead embryos and all sterile offspring (F2). These F2 sterile worms generally have an underproliferated germline and no-few gametes. The sterility and embryonic lethality displayed by null
pgl-1 mutants are temperature-sensitive, suggesting either that PGL-1 functions in a process that is intrinsically sensitive to temperature, or that there exists a partially redundant activity that can compensate for the loss of PGL-1 activity at permissive but not restrictive temperature. We predict that PGL-1 is an RNA-binding protein component of P granules, which is required for several aspects of germline development in C. elegans.