Core component of multiple cullin-5-RING E3 ubiquitin-protein ligase complexes (ECS complexes, also named CRL5 complexes), which mediate the ubiquitination and subsequent proteasomal degradation of target proteins (PubMed:11384984, PubMed:15601820, PubMed:21199876, PubMed:21980433, PubMed:23897481, PubMed:25505247, PubMed:27910872, PubMed:32200094, PubMed:33268465, PubMed:35512830, PubMed:38418882, PubMed:40963025). Acts a scaffold protein that contributes to catalysis through positioning of the substrate and the ubiquitin-conjugating enzyme (PubMed:11384984, PubMed:15601820, PubMed:33268465). The functional specificity of the E3 ubiquitin-protein ligase complex depends on the variable SOCS box-containing substrate recognition component (PubMed:11384984, PubMed:15601820, PubMed:33268465). Acts as a key regulator of neuron positioning during cortex development: component of various SOCS-containing ECS complexes, such as the ECS(SOCS7) complex, that regulate reelin signaling by mediating ubiquitination and degradation of DAB1 (By similarity). ECS(SOCS1) seems to direct ubiquitination of JAK2 (PubMed:11384984). The ECS(SOCS2) complex mediates the ubiquitination and subsequent proteasomal degradation of phosphorylated EPOR and GHR (PubMed:21980433, PubMed:25505247). The ECS(SPSB3) complex catalyzes ubiquitination of nuclear CGAS (PubMed:38418882). ECS(KLHDC1) complex is part of the DesCEND (destruction via C-end degrons) pathway and mediates ubiquitination and degradation of truncated SELENOS selenoprotein produced by failed UGA/Sec decoding, which ends with a glycine (PubMed:32200094). The ECS(ASB9) complex mediates ubiquitination and degradation of CKB (PubMed:33268465). As part of some ECS complex, promotes 'Lys-11'-linked ubiquitination and degradation of BTRC (PubMed:27910872). As part of a multisubunit ECS complex, polyubiquitinates monoubiquitinated POLR2A (PubMed:19920177). As part of the ECS(RAB40C) complex, mediates ANKRD28 ubiquitination and degradation, thereby inhibiting protein phosphatase 6 (PP6) complex activity and focal adhesion assembly during cell migration (PubMed:35512830). As part of the ECS(RAB40A) complex, mediates RHOU 'Lys-48'-linked ubiquitination and degradation, thus inhibiting focal adhesion disassembly during cell migration (PubMed:26598620). As part of the ECS(RAB40B) complex, mediates LIMA1/EPLIN and RAP2 ubiquitination, thereby regulating actin cytoskeleton dynamics and stress fiber formation during cell migration (PubMed:33999101, PubMed:35293963). The ECS(ASB7) complex acts a negative regulator of H3K9me3 histone mark by mediating ubiquitination and degradation of SUV39H1 (PubMed:40440427). As part of the ECS(LRRC58) complex, mediates CDO1 ubiquitination and degradation, regulating cysteine catabolism (PubMed:40963025). May form a cell surface vasopressin receptor (PubMed:9037604). {ECO:0000250|UniProtKB:Q9D5V5, ECO:0000269|PubMed:11384984, ECO:0000269|PubMed:15601820, ECO:0000269|PubMed:19920177, ECO:0000269|PubMed:21199876, ECO:0000269|PubMed:21980433, ECO:0000269|PubMed:23897481, ECO:0000269|PubMed:25505247, ECO:0000269|PubMed:26598620, ECO:0000269|PubMed:27910872, ECO:0000269|PubMed:32200094, ECO:0000269|PubMed:33268465, ECO:0000269|PubMed:33999101, ECO:0000269|PubMed:35293963, ECO:0000269|PubMed:35512830, ECO:0000269|PubMed:38418882, ECO:0000269|PubMed:40440427, ECO:0000269|PubMed:40963025, ECO:0000269|PubMed:9037604}. (Microbial infection) Following infection by HIV-1 virus, CUL5 associates with HIV-1 Vif proteins and forms a cullin-5-RING E3 ubiquitin-protein ligase complex (ECS complex) that catalyzes ubiquitination and degradation of APOBEC3F and APOBEC3G (PubMed:16636053, PubMed:22190037). The complex can also ubiquitinate APOBEC3H to some extent (PubMed:37640699). {ECO:0000269|PubMed:16636053, ECO:0000269|PubMed:22190037, ECO:0000269|PubMed:37640699}. (Microbial infection) Seems to be involved in proteasomal degradation of p53/TP53 stimulated by adenovirus E1B-55 kDa protein. . This is the function of CUL5 (cullin 5, Ensembl gene identifier ENSG00000166266).