Binds the poly(A) tail of mRNA. Appears to be an important mediator of the multiple roles of the poly(A) tail in mRNA biogenesis, stability and translation. In the cytoplasm, affects both translation and mRNA decay. Stimulates translation by interaction with translation initiation factor eIF4G, a subunit of the cap-binding complex eIF4F, bringing the 5'- and 3'-ends of the mRNA in proximity. The formation of this circular mRNP structure appears to be critical for the synergistic effects of the cap and the poly(A) tail in facilitating translation initiation, recycling of ribosomes, and mRNA stability. During infection with potyvirus TuMV, acts as a potential integral component of the viral replicase complex that could play an important role in the regulation of potyviral RNA-dependent RNA polymerase (RdRp). Binds to uridylated mRNAs and determines the size of uridine extensions (PubMed:26972004). Limits uridine extension by URT1, likely by binding to the oligo(A) tail and preventing URT1 access (PubMed:26972004). Interacts with eIF-iso4G. Interacts with ERD15/CID1 and CID7. Interacts with Turnip mosaic virus (TuMV) VPg-Pro and RNA-dependent RNA polymerase (RdRp). In TuMV-infected plants, partially retargeted in cytoplasmic virus-induced vesicles and in the nucleolus. Expressed in all organs (at the protein level) but under distinct spatial and temporal regulation within each organ. By potyvirus TuMV infection. Pab2 and pab4 double mutants, as well as pab2 and pab8 double mutants show significant growth and development defects and more resistance to Turnip mosaic virus (TuMV). A.thaliana contains 8 PABP genes. Belongs to the polyadenylate-binding protein type-1 family.