DNA- and RNA-binding protein involved in several cellular processes such as nuclear chromatin organization, telomere-length regulation, transcription, mRNA alternative splicing and stability, Xist-mediated transcriptional silencing and mitotic cell progression. Plays a role in the regulation of interphase large-scale gene-rich chromatin organization through chromatin-associated RNAs (caRNAs) in a transcription-dependent manner, and thereby maintains genomic stability. Required for the localization of the long non-coding Xist RNA on the inactive chromosome X (Xi) and the subsequent initiation and maintenance of X-linked transcriptional gene silencing during X-inactivation (By similarity). Required for the topoisomerase TOP2A protein stability and activity in a RNA-dependent manner (PubMed:20554522). Plays a role as a RNA polymerase II (Pol II) holoenzyme transcription regulator. Promotes transcription initiation by direct association with the core-TFIIH basal transcription factor complex for the assembly of a functional pre-initiation complex with Pol II in a actin-dependent manner. Blocks Pol II transcription elongation activity by inhibiting the C-terminal domain (CTD) phosphorylation of Pol II and dissociates from Pol II pre-initiation complex prior to productive transcription elongation. Positively regulates CBX5-induced transcriptional gene silencing and retention of CBX5 in the nucleus. Negatively regulates glucocorticoid-mediated transcriptional activation. Key regulator of transcription initiation and elongation in embryonic stem cells upon leukemia inhibitory factor (LIF) signaling. Involved in the long non-coding RNA H19-mediated Pol II transcriptional repression. Participates in the circadian regulation of the core clock component ARNTL/BMAL1 transcription. Plays a role in the regulation of telomere length. Plays a role as a global pre-mRNA alternative splicing modulator by regulating U2 small nuclear ribonucleoprotein (snRNP) biogenesis. Plays a role in mRNA stability. Component of the CRD-mediated complex that promotes MYC mRNA stabilization. Enhances the expression of specific genes, such as tumor necrosis factor TNFA, by regulating mRNA stability, possibly through binding to the 3'-untranslated region (UTR). Plays a role in mitotic cell cycle regulation. Involved in the formation of stable mitotic spindle microtubules (MTs) attachment to kinetochore, spindle organization and chromosome congression. Phosphorylation at Ser-58 by PLK1 is required for chromosome alignement and segregation and progression through mitosis. Contributes also to the targeting of AURKA to mitotic spindle MTs (By similarity). Binds to double- and single-stranded DNA and RNA, poly(A), poly(C) and poly(G) oligoribonucleotides (PubMed:20554522). Binds to chromatin-associated RNAs (caRNAs) (By similarity). Associates with chromatin to scaffold/matrix attachment region (S/MAR) elements in DNA (PubMed:8509422). Associates with chromatin in a chromatin-associated RNAs (caRNAs)-dependent manner. Binds to the Xist RNA. Binds the long non-coding H19 RNA. Binds to SMN1/2 pre-mRNAs at G/U-rich regions. Binds to small nuclear RNAs (snRNAs). Binds to the 3'-UTR of TNFA mRNA. Binds (via RNA-binding RGG-box region) to the long non-coding Xist RNA; this binding is direct and bridges the Xist RNA and the inactive chromosome X (Xi). Also negatively regulates embryonic stem cell differentiation upon LIF signaling. Required for embryonic development (By similarity). Binds to brown fat long non-coding RNA 1 (Blnc1); facilitates the recruitment of Blnc1 by ZBTB7B required to drive brown and beige fat development and thermogenesis (By similarity). Oligomer (via ATPase domain and RNA-binding RGG-box region); oligomerization occurs upon ATP-binding in a chromatin-associated RNAs (caRNAs)- and transcription-dependent manner and is required for chromatin decompaction. ATP hydrolysis is required to cycle from an oligomeric to monomeric state to compact chromatin. Component of the coding region determinant (CRD)-mediated complex, composed of DHX9, HNRNPU, IGF2BP1, SYNCRIP and YBX1. Identified in the spliceosome C complex. Identified in a IGF2BP1-dependent mRNP granule complex containing untranslated mRNAs. Associates with heterogeneous nuclear ribonucleoprotein (hnRNP) particles. Associates (via middle region) with the C-terminal domain (CTD) RNA polymerase II (Pol II) holoenzyme; this association occurs in a RNA-independent manner. Associates (via middle region) with the core-TFIIH basal transcription factor complex; this association inhibits the CTD phosphorylation of RNA polymerase II holoenzyme by down-regulating TFIIH kinase activity. Associates with the telomerase holoenzyme complex. Associates with spindle microtubules (MTs) in a TPX2-dependent manner. Interacts (via C-terminus) with actin; this interaction is direct and mediates association with the phosphorylated CTD of RNA polymerase II and is disrupted in presence of the long non-coding H19 RNA. Interacts with AURKA. Interacts (via C-terminus) with CBX5; this interaction is, at least in part, RNA-dependent. Interacts with CR2. Interacts with CRY1. Interacts (via C-terminus) with EP300; this interaction enhances DNA-binding to nuclear scaffold/matrix attachment region (S/MAR) elements. Interacts with ERBB4. Interacts with GEMIN5. Interacts with IGF2BP1. Interacts with IGF2BP2 and IGF2BP3. Interacts with NCL; this interaction occurs during mitosis. Interacts (via C-terminus) with NR3C1 (via C-terminus). Interacts with PLK1; this interaction induces phosphorylation of HNRNPU at Ser-58 in mitosis. Interacts with POU3F4. Interacts with SMARCA4; this interaction occurs in embryonic stem cells and stimulates global Pol II-mediated transcription (By similarity). Interacts (via C-terminus) with TOP2A; this interaction protects the topoisomerase TOP2A from degradation and positively regulates the relaxation of supercoiled DNA by TOP2A in a RNA-dependent manner (PubMed:20554522). Interacts with TPX2; this interaction recruits HNRNPU to spindle microtubules (MTs). Interacts with UBQLN2 (By similarity). Interacts (via RNA-binding RGG-box region) with ZBTB7B; the interaction facilitates the recruitment of long non-coding RNA Blnc1 by ZBTB7B (By similarity). Interacts with ERCC6 (By similarity). Localizes at inactive X chromosome (Xi) regions. Localizes in the nucleus during interphase. At metaphase, localizes with mitotic spindle microtubules (MTs). At anaphase, localizes in the mitotic spindle midzone. Localizes in spindle MTs proximal to spindle poles in a TPX2- and AURKA-dependent manner. The Ser-58 phosphorylated form localizes to centrosomes during prophase and metaphase, to mitotic spindles in anaphase and to the midbody during cytokinesis. Colocalizes with SMARCA4 in the nucleus (By similarity). Colocalizes with CBX5 in the nucleus. Colocalizes with NR3C1 in nuclear speckles. Localized in cytoplasmic ribonucleoprotein (RNP) granules containing untranslated mRNAs. The SAP domain is necessary for specific binding to nuclear scaffold/matrix attachment region (S/MAR) elements in DNA. The RNA-binding RGG-box region is necessary for its association with inactive X chromosome (Xi) regions and to chromatin-associated RNAs (caRNAs). Both the DNA-binding domain SAP and the RNA-binding RGG-box region are necessary for the localization of Xist RNA on the Xi. The ATPase and RNA-binding RGG-box regions are necessary for oligomerization. Cleaved at Asp-94 by CASP3 during T-cell apoptosis, resulting in a loss of DNA- and chromatin-binding activities. Extensively phosphorylated. Phosphorylated on Ser-58 by PLK1 and dephosphorylated by protein phosphatase 2A (PP2A) in mitosis. Arg-707 and Arg-713 are dimethylated, probably to asymmetric dimethylarginine (By similarity). Citrullinated by PADI4.