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Beschreibung

ATP-dependent RNA helicase DDX3X (UniProt: O00571, also known as EC:3.6.4.13, CAP-Rf, DEAD box protein 3 X-chromosomal, DEAD box X isoform, DBX, Helicase-like protein 2, HLP2) is encoded by the DDX3X (also known as DBX, DDX3) gene (Gene ID: 1654) in human. DDX3 is a ubiquitous cellular protein that is widely expressed in mammalian cells and is distributed throughout the cytoplasm and can also be found in the nucleus. It shuttles between the nucleus and the cytosol and is exported from the nucleus partly through the XPO1/CRM1 system and partly through NXF1/TAP. It serves as a multifunctional ATP-dependent RNA helicase and also displays ATPase activity that can be stimulated by various ribo-and deoxynucleic acids. It is also involved in many cellular processes, which do not necessarily require its ATPase/helicase catalytic activities. It is also involved in positive regulation of CDKN1A/p21 transcription in an SP1-dependent manner, hence can inhibit cell growth. This function of DDX3 requires its ATPase, but not the helicase activity. Independently of its ATPase activity, it can also promote the assembly of functional 80S ribosomes and disassembles from ribosomes prior to the translation elongation process. Although it is not involved in the general process of translation but is shown to promote efficient translation of selected complex mRNAs, containing highly structured 5'-untranslated regions (UTR). This function or DDX3 is dependent on its helicase activity. DDX3 is also involved in innate immunity, acting as a viral RNA sensor. It binds viral RNAs and promotes the production of interferon a and b . The cellular DDX3 is shown to be essential for hepatitis C virus (HCV) and HIV-1 replication. However, it inhibits hepatitis B virus transcription by its incorporation into nucleocapsids. During HCV infection, HCV core protein is reported to inhibit the interaction between MAVS and DDX3 and thus impairs MAVS-dependent INF- b induction. DDX3 can undergo phosphorylation by TBK1 and this phosphorylation is required for the synergistic induction of IFN-b mediated by TBK1 and DDX3. (Ref.: Geissler, R., et al. (2012). Nucl. Acid. Res. 40(11), 4998-5011, Angus, AGN., et al. (2010). J. Gen. Virol. 91, 122-132, Soulat, D., et al. (2008). EMBO J. 27(15), 2135-2146).