PROJECT SUMMARY/ABSTRACT Once thought to be a rare exception, it has become apparent over the past decade that long non-coding RNAs (lncRNAs) are quite common. Simply defined as RNA transcripts of more than 200 nt that do not encode proteins, lncRNAs have been shown to be important regulators of a plethora of biological processes, ranging from cellular proliferation to embryonic development. Initial studies have revealed that lncRNAs exert their functions through remarkably diverse mechanisms, acting as molecular scaffolds, guides, decoys and sequestration hubs. Tens of thousands of lncRNAs have been identified in the human and murine genome, but only a comparatively small number of them have been explored functionally. Indeed, it remains unclear how many of these lncRNAs carry out biological functions and how many are mere by-products of regulatory DNA elements. The identification and mechanistic analysis of biologically active lncRNAs is of considerable significance for human health, as such lncRNAs have the inherent potential to become novel therapeutic targets in the treatment of a variety of diseases, including viral infections and auto-immune disorders. The expression levels of thousands of lncRNAs are altered when immune cells are activated or virally infected, but their role in these processes has been investigated only in few instances. This application proposes to define the molecular mechanism that allows an HIV-responsive lncRNA to act as a selective regulator of cytokine levels in activated T cells. This will include a thorough characterization of the cytokine genes regulated by the lncRNA, as well as the identification of its DNA, RNA and protein interaction partners that mediate this function. The results from these experiments will be integrated into an updated model of cytokine regulation during T-cell activation. Additionally, a mouse carrying a conditional knockout allele of a previously unrecognized murine ortholog will be created and used to validate the role of this lncRNA in the function of primary T cells.