Substrate-recognition component of a Cul2-RING (CRL2) E3 ubiquitin-protein ligase complex of the DesCEND (destruction via C-end degrons) pathway, which recognizes a C-degron located at the extreme C terminus of target proteins, leading to their ubiquitination and degradation. The C-degron recognized by the DesCEND pathway is usually a motif of less than ten residues and can be present in full-length proteins, truncated proteins or proteolytically cleaved forms. The CRL2(FEM1B) complex specifically recognizes proteins ending with -Gly-Leu-Asp-Arg, such as CDK5R1, leading to their ubiquitination and degradation (By similarity). Also acts as a regulator of the reductive stress response by mediating ubiquitination of reduced FNIP1: in response to reductive stress, the CRL2(FEM1B) complex specifically recognizes a conserved Cys degron in FNIP1 when this degron is reduced, leading to FNIP1 degradation and subsequent activation of mitochondria to recalibrate reactive oxygen species (ROS) (By similarity). Promotes ubiquitination of GLI1, suppressing GLI1 transcriptional activator activity (By similarity). Promotes ubiquitination and degradation of ANKRD37 (By similarity). Promotes ubiquitination and degradation of SLBP. Involved in apoptosis by acting as a death receptor-associated protein that mediates apoptosis (By similarity). Also involved in glucose homeostasis in pancreatic islet (By similarity). May also act as an adapter/mediator in replication stress-induced signaling that leads to the activation of CHEK1 (By similarity). Protein modification; protein ubiquitination. Component of a CRL2 E3 ubiquitin-protein ligase complex, also named ECS (Elongin BC-CUL2/5-SOCS-box protein) complex, composed of CUL2, Elongin BC (ELOB and ELOC), RBX1 and substrate-specific adapter FEM1B. Homooligomer. Interacts with PPM1F and PHTF1. Interacts with the death domain of FAS/TNFRSF6 and TNFRSF1A. Interacts with CHEK1 (By similarity). Interacts with NKX3-1 (By similarity). In the nucleus, the protein level increased slightly after camptothecin (CPT) treatment. Associated with chromatin. Present in adult testis (at protein level). In testis, it is first observed in leptotene and early pachytene spermatocytes. Present at high level in pachytene spermatocytes at stage IX-X and persists throughout spermiogenesis. At spermiation, most of the protein is associated with the residual bodies, but some protein persists in the queues of mature spermatids. Belongs to the fem-1 family.