DDX21
Description
The DDX21 (DExD-box helicase 21) is a protein-coding gene located on chromosome 10.
Nucleolar RNA helicase 2 is an enzyme that in humans is encoded by the DDX21 gene.
== Function == DEAD box proteins, characterized by the conserved motif Asp-Glu-Ala-Asp (DEAD), are putative RNA helicases. They are implicated in a number of cellular processes involving alteration of RNA secondary structure such as translation initiation, nuclear and mitochondrial splicing, and ribosome and spliceosome assembly. Based on their distribution patterns, some members of this family are believed to be involved in embryogenesis, spermatogenesis, and cellular growth and division. This gene encodes a DEAD box protein, which is an antigen recognized by autoimmune antibodies from a patient with watermelon stomach disease. This protein unwinds double-stranded RNA, folds single-stranded RNA, and may play important roles in ribosomal RNA biogenesis, RNA editing, RNA transport, and general transcription.
== Interactions == DDX21 has been shown to interact with C-jun.
DDX21 is a RNA helicase that acts as a sensor of the transcriptional status of both RNA polymerase I and II. It promotes ribosomal RNA (rRNA) processing and transcription from polymerase II. DDX21 binds various RNAs, including rRNAs, snoRNAs, 7SK RNA, and, to a lesser extent, mRNAs. In the nucleolus, it localizes to the rDNA locus, where it directly binds rRNAs and snoRNAs, and promotes rRNA transcription, processing, and modification. DDX21 is required for rRNA 2'-O-methylation, possibly by promoting the recruitment of late-acting snoRNAs SNORD56 and SNORD58 with pre-ribosomal complexes. In the nucleoplasm, it binds 7SK RNA and is recruited to the promoters of Pol II-transcribed genes, where it facilitates the release of P-TEFb from inhibitory 7SK snRNP, promoting transcription of target genes. DDX21 functions as a cofactor for JUN-activated transcription, being required for phosphorylation of JUN at 'Ser-77'. It can unwind double-stranded RNA (helicase) and fold or introduce a secondary structure to a single-stranded RNA (foldase). Together with SIRT7, DDX21 prevents R-loop-associated DNA damage and transcription-associated genomic instability by activating the helicase activity through SIRT7 deacetylation, overcoming R-loop-mediated stalling of RNA polymerases. DDX21 is involved in rRNA processing and may bind to specific miRNA hairpins. It is a component of a multi-helicase-TICAM1 complex that acts as a cytoplasmic sensor of viral double-stranded RNA (dsRNA), playing a role in the activation of antiviral responses, including the induction of pro-inflammatory cytokines via the adapter molecule TICAM1.
DDX21 is also known as GUA, GURDB, II/Gu, RH, RH II/Gu, RH-II/GU, RH-II/GuA, gu-alpha.
