Novel isoforms RXRalpha2 and RXRalpha3 of a nuclear receptor RXRalpha. Different from a known isoform RXRalpha1, the transcriptional activation effects of RXRalpha2 and RXRalpha3 are elevated by SRC-1. A method of evaluating the function of enhancing the transcriptional activation effect by a coactivator of these RXRalpha isoforms and a screening method based on this evaluation method are provided. By controlling the interaction with each coactivator, the transcription-controlling activity can be isoform-specifically regulated.
