Recent studies have identified coactivators that function with the nonsteroid nuclear hormone receptors. These proteins have histone acetyltransferase activity and appear to contribute to transcriptional regulation by nuclear receptors through remodeling of chromatin. However not all nuclear receptors activate genes that contain DNA elements that they recognize. Such specificity seemed not to come from known coactivators because the coactivators appear to interact with all active nuclear hormone receptors. Now, Li et al. have identified a new coactivator they call NRIF3 (for nuclear receptor-interacting factor 3) that has very little sequence similarity to previously identified coactivators. And unlike other coactivators, NRIF3 potentiates only transcription mediated by thyroid hormone receptors and retinoid X receptors, not that induced by other nonsteroid receptors. Thus, NRIF3 may represent a new class of coactivators that work together with the receptors and general coactivators to generate receptor-specific regulation.
Li D., Desai-Yajnik V., Lo E., Schapira M., Abagyan R., and Samuels H.H. (1999) NRIF3 is a novel coactivator mediating functional specificity of nuclear hormone receptors. Mol. Cell. Biol. 19:7191-7202. [Abstract]