RNA-binding protein that plays a role in the regulation of transcription, pre-mRNA splicing and mRNA translation (PubMed:14699138, PubMed:16455055, PubMed:19523114, PubMed:21771594). Negatively regulates DNA-binding activity of the transcription factor MEF2C in myocardial cells in response to mechanical stress (By similarity). Plays a role in pre-mRNA splicing regulation (PubMed:19523114). Binds (via C-terminus) to poly(U) RNA (PubMed:19523114). Involved in mRNA translation regulation, probably at the initiation step (PubMed:21771594). Seems to play a role in PML-nuclear bodies formation (PubMed:28695742). Associates with polysomes (PubMed:21771594). Interacts with FMR1 (PubMed:21771594). Interacts with FXR1 and FXR2 (PubMed:21771594). Interacts with CHD3 (via C-terminus) (PubMed:12505151). Interacts (via C-terminus) with RACK1 (PubMed:14699138). Interacts with p53/TP53 (PubMed:16455055). Interacts (via N-terminus) with SRSF9; this interaction is direct (PubMed:19523114). Interacts with SYNCRIP; this interaction is direct (PubMed:19523114). Interacts with MEF2C (via N-terminus); this interaction decreases DNA-binding activity of MEF2C in myocardial cells in response to mechanical stress (PubMed:15862299). Interacts with PRMT1 (via N-terminus) (PubMed:16879614). Interacts with SPIN1 (By similarity). Transported into the nuclear compartment in activated leukocytes (PubMed:9523163). Inhibition of methylation alters its distribution between the nuclear and cytoplasmic compartments (PubMed:16879614, PubMed:19523114). Methylation may be required for its localization in subnuclear structures, such as nucleoli, nuclear speckles, Cajal bodies and Gemini of coiled bodies (gems) (PubMed:19523114). Colocalizes with FMR1, FXR1 and FXR2 in cytoplasmic stress granules (PubMed:21771594). In myocardial cells, localization at the sarcoplasm is reduced in response to mechanical stress (By similarity). Highly expressed in brain, heart, and kidney, and moderately expressed in skeletal muscle. Also expressed in a variety of tumor cell lines and in activated but not resting leukocytes. The C-terminal region is necessary for nucleus and cytoplasmic localization (PubMed:19523114). The N-terminal region is necessary for nucleus and nuclear bodies localization (PubMed:19523114). Regions containing Arg-Gly-Gly repeats (RGG/RXR-box) may be preferentially methylated by PRMT1 (PubMed:16879614). Methylated (PubMed:16879614). Methylation is decreased by phorbol 12-myristate 13-acetate (PMA)-activated PKC, in vitro (PubMed:16879614). Phosphorylated by phorbol 12-myristate 13-acetate (PMA)-activated PKC isoforms at Thr-354 and Thr-375. Able to bind hyaluronan. However, its intracellular localization suggests that this interaction may not be relevant in vivo. The interaction with RACK1 is abolished upon activation of L540 tumor cells with PMA, which results in phosphorylation and exit of HABP4 from the nucleus.