The USA-derived transcriptional coactivator PC2 is a submodule of TRAP/SMCC and acts synergistically with other PCs

PC2, the high-molecular weight constituent of the potent USA transcriptiona l coactivator fraction, was identified as a Mediator-like complex. Its comp osition resembles that of the TRAP/SMCC complex, but PC2 is distinguished b y the prominent absence of the SRB10 and SRB11 kinase/cyclin pair, as well as several additional polypeptides. Furthermore, affinity-purified PC2, whi ch lacks independent activity, acts in synergy with USA-derived coactivator s PC3/topoisomerase I and PC4 to mediate the effects of a variety of activa tors (including VP16, the synthetic activator GAL4-AH, and the orphan nucle ar receptor HNF4) and thus recapitulates partial USA coactivator function.