Enables DNA-binding transcription repressor activity, RNA polymerase II-specific and RNA polymerase II transcription regulatory region sequence-specific DNA binding activity. Acts upstream of or within negative regulation of transcription by RNA polymerase II. Located in nucleus. Is expressed in genitourinary system; heart; and lung. Orthologous to human BCL6B (BCL6B transcription repressor). [provided by Alliance of Genome Resources, Apr 2022]