| Poly(A)‑binding protein 1 (PABP1) is a core RNP‑associated RNA‑binding protein that binds the 3ʹ‑poly(A) tails of nuclear and cytoplasmic mRNAs and interacts directly with the eIF4G subunit of the eIF4F complex, thereby contributing to mRNA circularization, translation initiation, and mRNA stabilization while also participating in regulated mRNA turnover and microRNA‑dependent silencing pathways. PABP1 contains multiple RNA recognition motifs that form a compact, highly flexible tandem array that wraps around poly(A) and engages the N‑terminal and C‑terminal regions of the protein, including an unstructured linker domain where arginine residues 455 and 460 reside as part of a methylation‑rich segment recognized by arginine methyltransferases. PABP1 is methylated at Arg455 and Arg460 by CARM1 (PRMT4), which catalyzes asymmetric dimethylation of these sites in vitro and in vivo, and the same region is also subject to additional type‑1 arginine methylation in certain cell types, suggesting that the methylation state of this patch can be modulated by a combination of PRMT activities. These arginine methylation events occur in a domain that participates in protein–protein interactions, including with components of the translation apparatus, and methylation at Arg455/Arg460 influences the broader methylation landscape of PABP1, although methylation per se does not strongly alter PABP1 abundance or steady‑state cytoplasmic localization in standard culture models. PABP1 also shuttles between the nucleus and cytoplasm, where its phosphorylation enhances RNA‑binding affinity and modulates its association with mRNA‑processing and translation‑initiation complexes, and its methylation status has been adopted as a cellular readout for CARM1 activity in chemical‑probe and inhibitor studies. |
Lane 1: HCT116, Lane 2: C6, Lane 3: COS
