PABPC

Poly(A) binding protein cytoplasmic (PABPC) is a family of RNA-binding proteins that associate with the poly(A) tail of cytoplasmic mRNAs in eukaryotic cells. By binding poly(A) sequences, PABPC influences mRNA stability and translational efficiency, in part by promoting a closed-loop mRNA conformation through interactions with the cap-binding initiation machinery, notably eIF4G. This bridging supports efficient translation initiation and ribosome recycling, and can modulate mRNA decay by coordinating deadenylation with decay factors.

Structural features: PABPC proteins typically contain four RNA recognition motif domains (RRM1-4) in the N-terminal region that bind poly(A) RNA, followed by a C-terminal MLLE (PABC) domain that mediates protein–protein interactions with PAM2-containing partners such as eIF4G, Paip1/2, and PAN3. These interactions enable PABPC to function as a dynamic hub linking poly(A) tails to translation and decay pathways.

Genomics and evolution: In vertebrates, several PABPC genes exist; PABPC1 encodes the canonical cytoplasmic poly(A) binding protein, while PABPC3, PABPC4, and PABPC5 show tissue-specific expression or specialized roles. Orthologs are present across eukaryotes, including yeast Pab1p, reflecting a deeply conserved function in post-transcriptional regulation.

Function and regulation: PABPC participates in mRNA stabilization, translation initiation, and subcellular localization. Its activity is modulated by cellular signaling, developmental stage, and interactions with microRNA pathways, making it a central regulator of gene expression at the post-transcriptional level.