Probable receptor which is required for the oocyte-to-zygote transition although its exact function is controversial (PubMed:16360684, PubMed:20971008). Redundantly with egg-2, seems to be required for fertilization probably by promoting the interaction or fusion between sperm and oocyte (PubMed:16360684). Conversely, shown to be dispensable for fertilization but required together with egg-2 for the formation of a continuous and cohesive eggshell chitin layer by maintaining a homogenous distribution of chitin synthase chs-1 at the unfertilized oocyte cell membrane (PubMed:20971008). Appears to recruit or maintain together to the unfertilized oocyte cortex several proteins including chs-1, kinase mbk-2 and pseudophosphatases egg-3, and possibly egg-4 and egg-5 (PubMed:20971008). Localizes to the cell membrane of developing oocytes (PubMed:16360684, PubMed:20971008). Plasma membrane localization requires extracellular matrix protein cbd-1 (PubMed:20971008). After fertilization, localizes to endosomes in zygotes (PubMed:20971008). Specifically expressed in developing oocytes of adult germ line. Temperature sensitive phenotype with severe sterility at the restrictive temperature of 25 degrees Celsius (PubMed:16360684, PubMed:20971008). Zygotes exit the spermatheca with a pinched morphology and leave a trailing section behind and are polyspermic (PubMed:20971008). The eggshell chitin layer is fragmented and often accumulates at one end of the embryo (PubMed:20971008). Ovulation is severely reduced resulting in oocyte accumulation in the gonad and a disappearance of sperm in the spermatheca (PubMed:16360684). Conversely, although sperm and oocyte appear to make contact in the spermatheca no visible fertilization occurs and endomitotic oocytes accumulate with age (PubMed:16360684). Male fertility is not affected (PubMed:16360684). Simultaneous RNAi-mediated knockdown with egg-2 results in complete sterility (PubMed:16360684). In unfertilized oocytes, disrupts the homogenous distribution of cortical chitin synthase chs-1, pseudophosphatase egg-3 and kinase mbk-2 (PubMed:20971008).