Enables DNA-binding transcription activator activity, RNA polymerase II-specific; RNA polymerase II cis-regulatory region sequence-specific DNA binding activity; and WD40-repeat domain binding activity. Involved in positive regulation of transcription by RNA polymerase II. Acts upstream of or within several processes, including cellular response to cytokine stimulus; embryonic digestive tract development; and hematopoietic or lymphoid organ development. Located in cytosol and nucleus. Is expressed in several structures, including alimentary system; brain; genitourinary system; limb; and sensory organ. Used to study essential thrombocythemia and myelofibrosis. Orthologous to human MYB (MYB proto-oncogene, transcription factor). [provided by Alliance of Genome Resources, Apr 2022]