mRNA-binding component of ribonucleosomes. Specifically binds AU-rich element (ARE)-containing mRNAs. Involved in post-transcriptional regulation of cytokines mRNAs. Component of ribonucleosomes. Phosphorylated at Ser-84 by MAPKAPK2 in response to LPS treatment, promoting stabilization of GADD45A mRNA. Arg-291 is dimethylated, probably to asymmetric dimethylarginine.