GO:0001225:   RNA polymerase II transcription coactivator binding
Interacting selectively and non-covalently with an RNA polymerase II transcription coactivator, any protein involved in positive regulation of transcription of RNA polymerase II via protein-protein interactions with transcription factors and other proteins that positively regulate transcription. Transcription coactivators do not bind DNA directly, but rather mediate protein-protein interactions between activating transcription factors and the basal transcription machinery of RNA polymerase II.