4nbo
Human steroid receptor RNA activator protein carboxy-terminal domain
Structural highlights
FunctionSRA1_HUMAN Functional RNA which acts as a transcriptional coactivator that selectively enhances steroid receptor-mediated transactivation ligand-independently through a mechanism involving the modulating N-terminal domain (AF-1) of steroid receptors. Also mediates transcriptional coactivation of steroid receptors ligand-dependently through the steroid-binding domain (AF-2). Enhances cellular proliferation and differentiation and promotes apoptosis in vivo. May play a role in tumorigenesis.[1] [2] [3] [4] [5] Publication Abstract from PubMedIn a widely accepted model, the steroid receptor RNA activator protein (SRA protein; SRAP) modulates the transcriptional regulatory activity of SRA RNA by binding a specific stem-loop of SRA. We first confirmed that SRAP is present in the nucleus as well as the cytoplasm of MCF-7 breast cancer cells, where it is expressed at the level of about 10(5) molecules per cell. However, our SRAP-RNA binding experiments, both in vitro with recombinant protein and in cultured cells with plasmid-expressed protein and RNA, did not reveal a specific interaction between SRAP and SRA. We determined the crystal structure of the carboxy-terminal domain of human SRAP and found that it does not have the postulated RRM (RNA recognition motif). The structure is a five-helix bundle that is distinct from known RNA-binding motifs and instead is similar to the carboxy-terminal domain of the yeast spliceosome protein PRP18, which stabilizes specific protein-protein interactions within a multisubunit mRNA splicing complex. SRA binding experiments with this domain gave negative results. Transcriptional regulation by SRA/SRAP was examined with siRNA knockdown. Effects on both specific estrogen-responsive genes and genes identified by RNA-seq as candidates for regulation were examined in MCF-7 cells. Only a small effect (~20% change) on one gene resulting from depletion of SRA/SRAP could be confirmed. We conclude that the current model for SRAP function must be reevaluated; we suggest that SRAP may function in a different context to stabilize specific intermolecular interactions in the nucleus. Structure and function of steroid receptor RNA activator protein, the proposed partner of SRA noncoding RNA.,McKay DB, Xi L, Barthel KK, Cech TR J Mol Biol. 2014 Apr 17;426(8):1766-85. doi: 10.1016/j.jmb.2014.01.006. Epub 2014, Jan 30. PMID:24486609[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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