Enables RNA polymerase II cis-regulatory region sequence-specific DNA binding activity and transcription coactivator activity. Acts upstream of or within circadian rhythm. Part of mediator complex. Is expressed in brain; branchial arch; genitourinary system; limb; and retina nuclear layer. Orthologous to human THRAP3 (thyroid hormone receptor associated protein 3). [provided by Alliance of Genome Resources, Apr 2022]