Enables DNA-binding transcription activator activity, RNA polymerase II-specific and RNA polymerase II cis-regulatory region sequence-specific DNA binding activity. Involved in heart development; positive regulation of gap junction assembly; and positive regulation of transcription by RNA polymerase II. Acts upstream of or within several processes, including cell communication involved in cardiac conduction; heart development; and positive regulation of cell population proliferation. Located in nucleus. Part of transcription regulator complex. Is expressed in several structures, including embryo mesenchyme; eye; genitourinary system; heart; and vena cava. Used to study Holt-Oram syndrome. Human ortholog(s) of this gene implicated in Holt-Oram syndrome. Orthologous to human TBX5 (T-box transcription factor 5). [provided by Alliance of Genome Resources, Apr 2022]