Figure 1.

RNA helicase DDX21 exerts a multitude of functions at various locations within the cell

DDX21 holds important functions in ribosomal RNA (rRNA) production and processing in the nucleolus. The RNA helicase also plays a role in the nucleoplasm, where DDX21 acts as a regulator of Pol II-mediated transcription to control gene expression. At promoters, DDX21 stimulates transcription via direct interactions with TFs and binding to the 7SK snRNP complex. DDX21 facilitates the release of P-TEFb from the 7SK snRNP and enables commencement of effective transcription elongation. DDX21 can also binds to mRNAs in the nucleoplasm, which is speculated to have an impact on transcript stability, processing, translation, and/or nuclear export. DDX21 localization, binding, and function are affected by a variety of signal-responsive proteins, including TFs such as PGR and phosphatases such as PLR3. Red arrows indicate the effects of nucleotide stress on the processes associated with DDX21.