DNA-binding transcription factor (PubMed:34936696, PubMed:40608935). Also acts as an atypical E3 ubiquitin-protein ligase that mediates 'Lys-63'-linked ubiquitination of MAP3K14/NIK, leading to stabilize and activate MAP3K14/NIK (PubMed:20682767). It thereby acts as an activator of the non-canonical NF-kappa-B2/NFKB2 pathway (PubMed:20682767). May also play an important role in cell proliferation and/or anti-apoptosis (PubMed:12738986). {ECO:0000269|PubMed:12738986, ECO:0000269|PubMed:20682767, ECO:0000269|PubMed:34936696, ECO:0000269|PubMed:40608935}. This is the function of ZFP91 (ZFP91 zinc finger protein, atypical E3 ubiquitin ligase, Ensembl gene identifier ENSG00000186660).