Enables PDZ domain binding activity and bHLH transcription factor binding activity. Contributes to E-box binding activity. Involved in positive regulation of gene expression and positive regulation of transcription, DNA-templated. Part of transcription regulator complex. Human ortholog(s) of this gene implicated in agammaglobulinemia and colorectal cancer. Orthologous to human TCF3 (transcription factor 3). [provided by Alliance of Genome Resources, Apr 2022]