Enables transcription coactivator activity. Acts upstream of or within several processes, including defense response to other organism; hematopoietic or lymphoid organ development; and regulation of gene expression. Predicted to be located in several cellular components, including cytosol; midbody; and nucleoplasm. Predicted to be part of Bcl3-Bcl10 complex and Bcl3/NF-kappaB2 complex. Is expressed in several structures, including alimentary system; early conceptus; genitourinary system; immune system; and liver and biliary system. Orthologous to human BCL3 (BCL3 transcription coactivator). [provided by Alliance of Genome Resources, Apr 2022]