Component of an E3 ubiquitin-protein ligase that includes cul4 (By similarity). Required for ubiquitination and the subsequent degradation of the DNA replication licensing factor cdt1 and of the ribonucleotide reductase inhibitor spd1. Also required for transcription-coupled nucleotide excision repair. Protein modification; protein ubiquitination. Interacts with csn1, csn2, cdt2, ckn1, iqw1 and wdr21. Belongs to the DDB1 family.