Enables estrogen receptor binding activity and histone kinase activity (H2A-T120 specific). Involved in cell competition in a multicellular organism; histone H2A-T120 phosphorylation; and negative regulation of transcription by RNA polymerase II. Located in fibrillar center and nucleoplasm. Part of Cul4-RING E3 ubiquitin ligase complex. Colocalizes with COP9 signalosome. [provided by Alliance of Genome Resources, Apr 2022]