Enables RNA polymerase II-specific DNA-binding transcription factor binding activity and transcription coregulator activity. Involved in several processes, including neuronal stem cell population maintenance; positive regulation of transcription by RNA polymerase II; and regionalization. Located in euchromatin and nucleus. Part of super elongation complex. Is expressed in several structures, including brain; large field neurons; nerve; presumptive embryonic/larval system; and synaptic neuropil domain. Used to study type 2 diabetes mellitus. Human ortholog(s) of this gene implicated in KINSSHIP syndrome and X-linked intellectual developmental disorder 109. Orthologous to several human genes including AFF2 (ALF transcription elongation factor 2); AFF3 (ALF transcription elongation factor 3); and AFF4 (ALF transcription elongation factor 4).