Heterogenous nuclear ribonucleoprotein (hnRNP) implicated in mRNA processing mechanisms. Component of the CRD-mediated complex that promotes MYC mRNA stability. Is associated in vitro with pre-mRNA, splicing intermediates and mature mRNA protein complexes. Binds to apoB mRNA AU-rich sequences. Part of the APOB mRNA editosome complex and may modulate the postranscriptional C to U RNA-editing of the APOB mRNA through either by binding to A1CF (APOBEC1 complementation factor), to APOBEC1 or to RNA itself. May be involved in translationally coupled mRNA turnover. Implicated with other RNA-binding proteins in the cytoplasmic deadenylation/translational and decay interplay of the FOS mRNA mediated by the major coding-region determinant of instability (mCRD) domain. Interacts in vitro preferentially with poly(A) and poly(U) RNA sequences. May be involved in cytoplasmic vesicle-based mRNA transport through interaction with synaptotagmins (By similarity). Identified in a histone pre-mRNA complex, at least composed of ERI1, LSM11, SLBP, SNRPB, SYNCRIP and YBX1. Identified in the spliceosome C complex (By similarity). Component of the coding region determinant (CRD)-mediated complex, composed of DHX9, HNRNPU, IGF2BP1, SYNCRIP and YBX1. Identified in a mRNP complex, at least composed of DHX9, DDX3X, ELAVL1, HNRNPU, IGF2BP1, ILF3, PABPC1, PCBP2, PTBP2, STAU1, STAU2, SYNCRIP and YBX1. Identified in a mRNP granule complex, at least composed of ACTB, ACTN4, DHX9, ERG, HNRNPA1, HNRNPA2B1, HNRNPAB, HNRNPD, HNRNPL, HNRNPR, HNRNPU, HSPA1, HSPA8, IGF2BP1, ILF2, ILF3, NCBP1, NCL, PABPC1, PABPC4, PABPN1, RPLP0, RPS3, RPS3A, RPS4X, RPS8, RPS9, SYNCRIP, YBX1 and untranslated mRNAs. Component of the APOB mRNA editosome. Interacts with APOBEC1 and A1CF. Part of a complex associated with the FOS mCRD domain and consisting of PABPC1, PAIP1, CSDE1/UNR, HNRPD and SYNCRIP. Interacts with HNRPR, SMN, POLR2A hyperphosphorylated C-terminal domain, minute virus of mice (MVM) NS1 protein and through its C-terminal domain with SYT7, SYT8 and SYT9. The non-phosphorylated and phosphorylated forms are colocalized with PAIP1 in polysomes. Interacts with GTPBP1 (By similarity). Interacts with HABP4 (By similarity). Localized in cytoplasmic mRNP granules containing untranslated mRNAs (By similarity). Expressed predominantly in the nucleoplasm. The tyrosine phosphorylated form bound to RNA is found in microsomes (By similarity). The domain containing eight Arg-Gly-Gly repeats (RGG/RXR-box) may be involved in RNA-binding and protein-protein interactions. It is methylated by PRMT1, and essential for nuclear localization (By similarity). Phosphorylated on tyrosine. The membrane-bound form found in microsomes is phosphorylated in vitro by insulin receptor tyrosine kinase (INSR). Phosphorylation is inhibited upon binding to RNA, whereas the cytoplasmic form is poorly phosphorylated.