Ubiquitin-binding protein which acts as an adapter for ATPase cdc-48.1 and/or cdc-48.2, conferring substrate specificity (PubMed:20977550). Together with ubxn-2 and ubxn-3, plays a role in hermaphrodite spermatogenesis probably by promoting the degradation of sex determination terminal factor tra-1. Interacts with cdc-48.1 (via N-terminus) and cdc-48.2 (via N-terminus) in vitro; the interaction with cdc-48.1 is not detected in vivo. Colocalizes with cdc-48.1 to the perinuclear region in spermatocytes. Expressed in the germline (at protein level) (PubMed:17498661, PubMed:20977550). Expressed in spermatocytes but not in mature sperm (at protein level) (PubMed:20977550). Ubiquitously expressed (PubMed:17498661). Predominantly expressed in the spermatheca (PubMed:17498661). Expressed in embryos, L4 larvae and adults. Expressed to a lesser extent between L1 and L3 larval stages. RNAi-mediated knockdown does not cause any visible phenotype. Simultaneous RNAi-mediated knockdown of ubxn-2 and ubxn-3, causes 50 percent embryonic lethality. The surviving hermaphrodite progeny are sterile due to a lack of sperm. Abnormal accumulation of sex determination terminal factor tra-1. Germline development is normal. In males, sperm production is normal.