Substrate-recognition component of two distinct E3 ligase complexes, the SKP1-CUL1-FBXO44 complex and the CUL4B-DDB1-FBXO44 complex (PubMed:18203720, PubMed:25970626). The complex SCF(FBXO44) complex ubiquitinates and mediates BRCA1 degradation (PubMed:23086937). In association with cullin 4B/CUL4B and DDB1, mediates the ubiquitination of RGS2 leading to its degradation (PubMed:25970626). Additionally, regulates the pregnane X receptor/NR1I2 protein level by ubiquitination and degradation (PubMed:37969738). {ECO:0000269|PubMed:23086937, ECO:0000269|PubMed:25970626, ECO:0000269|PubMed:37969738}. This is the function of FBXO44 (F-box protein 44, Ensembl gene identifier ENSG00000132879).