Nuclear receptor coactivator genes encode a class of proteins that are recruited and serve as bridging molecules between the transcription initiation complex and nuclear receptors (NRs). Most of these coactivators interact with the AF-2 domain of NRs through one or several LXXLL motifs called NR box. Members of NRs includes the 5 steroid receptors and class II nuclear receptors. After binding to enhancer elements, transcription factors require transcriptional coactivator proteins to mediate their stimulation of transcription initiation. (NCI) [ ]