Binds the poly(A) tail of mRNA, including that of its own transcript, and regulates processes of mRNA metabolism such as pre-mRNA splicing and mRNA stability (PubMed:11051545, PubMed:17212783, PubMed:25480299). Its function in translational initiation regulation can either be enhanced by PAIP1 or repressed by PAIP2 (PubMed:11051545, PubMed:20573744). Can probably bind to cytoplasmic RNA sequences other than poly(A) in vivo. Binds to N6-methyladenosine (m6A)-containing mRNAs and contributes to MYC stability by binding to m6A-containing MYC mRNAs (PubMed:32245947). Involved in translationally coupled mRNA turnover (PubMed:11051545). Implicated with other RNA-binding proteins in the cytoplasmic deadenylation/translational and decay interplay of the FOS mRNA mediated by the major coding-region determinant of instability (mCRD) domain (PubMed:11051545). Involved in regulation of nonsense-mediated decay (NMD) of mRNAs containing premature stop codons; for the recognition of premature termination codons (PTC) and initiation of NMD a competitive interaction between UPF1 and PABPC1 with the ribosome-bound release factors is proposed (PubMed:18447585). By binding to long poly(A) tails, may protect them from uridylation by ZCCHC6/ZCCHC11 and hence contribute to mRNA stability (PubMed:25480299). (Microbial infection) Positively regulates the replication of dengue virus (DENV). May form homodimers. Component of a multisubunit autoregulatory ribonucleoprotein complex (ARC), at least composed of IGF2BP1, PABPC1 and CSDE1 (PubMed:16356927). Directly interacts with IGF2BP1; the interaction is enhanced by SEPIN14P20 peptide RBPR (PubMed:32245947, PubMed:29476152). Part of a complex associated with the FOS mCRD domain and consisting of HNRPD, SYNCRIP, PAIP1 and CSDE1/UNR (PubMed:11051545). Interacts with the PABPC1-interacting motif-1 (PAM1) and -2 (PAM2) of PAIP1 and PAIP2 (PubMed:9548260, PubMed:11172725, PubMed:11438674, PubMed:11997512, PubMed:11287632, PubMed:20096703, PubMed:33876849). Interacts with PAIP1 with a 1:1 stoichiometry and with PAIP2 with a 1:2 stoichiometry. The interaction with CSDE1 is direct and RNA-independent. Found in a mRNP complex with YBX2 (By similarity). Interacts with TENT2/GLD2 (By similarity). Identified in the spliceosome C complex (PubMed:11991638). Identified in a mRNP complex, at least composed of DHX9, DDX3X, ELAVL1, HNRNPU, IGF2BP1, ILF3, PABPC1, PCBP2, PTBP2, STAU1, STAU2, SYNCRIP and YBX1. The interaction with DDX3X is direct and RNA-independent (PubMed:18596238, PubMed:21883093, PubMed:22872150). This interaction increases in stressed cells and decreases during cell recovery (PubMed:21883093). Identified in a IGF2BP1-dependent mRNP granule complex containing untranslated mRNAs. Interacts with NXF1/TAP (PubMed:17267499, PubMed:18596238). Interacts with PIWIL1 (By similarity). Interacts with AGO1, AGO2, GSPT1 and GSPT2 (PubMed:17932509, PubMed:18447585, Ref.62). Interacts with LARP4B (Ref.64). Interacts (via the second and third RRM domains and the C-terminus) with PAIP2B (via central acidic portion and C-terminus) (PubMed:16804161, PubMed:11287632). Forms a complex with LARP1 and SHFL (PubMed:20430826, PubMed:24532714, PubMed:25940091, PubMed:26735137). Interacts with LARP4 (PubMed:21098120). Interacts with ZFC3H1 in a RNase-sensitive manner (PubMed:27871484). Interacts with TRIM71 (via NHL repeats) in an RNA-dependent manner (PubMed:23125361). Interacts with TENT5C; the interaction has no effect on TENT5C poly(A) polymerase function (PubMed:28931820). Interacts with G3BP1 and G3BP2 (PubMed:23279204). Interacts with ENDOV; the interaction is RNA-dependent and stimulates ENDOV activity (PubMed:27573237). Interacts with UPF1; the interaction is RNA-dependent (PubMed:25220460). Interacts with IGF2BP2 and IGF2BP3 (PubMed:29476152). May interact with SETX (PubMed:21700224). (Microbial infection) Interacts (via C-terminus) with human cytomegalovirus/HHV-5 protein UL69. (Microbial infection) Interacts (via C-terminus) with human respiratory syncytial virus (HRSV) M2-1 protein. Localized in cytoplasmic mRNP granules containing untranslated mRNAs (PubMed:17289661). Shuttles between the cytoplasm and the nucleus (PubMed:9582337). During stress and in the absence of DDX3X, localizes to the nucleus (PubMed:21883093). At the leading edge of migrating fibroblasts, colocalizes with DDX3X (PubMed:28733330). Relocalizes to cytoplasmic stress granules upon cellular stress where it colocalizes with ENDOV (PubMed:27573237). In case of HRSV infection, localizes in cytoplasmic inclusion bodies substructures called inclusion bodies associated granules (IBAGs) (PubMed:31649314). Ubiquitous. The RNA-binding domains RRM1 and RRM2 and the C-terminus (last 138 amino acids) regions interact with the PABPC1-interacting motif-1 (PAM1) and -2 (PAM2) of PAIP1, respectively. The RNA-binding domains RRM2 and RRM3 and the C-terminus (last 138 amino acids) regions interact with the PABPC1-interacting motif-1 (PAM1) and -2 (PAM2) of PAIP2, respectively. Phosphorylated by MAPKAPK2. Methylated by CARM1. Arg-493 is dimethylated, probably to asymmetric dimethylarginine. Many viruses shutoff host mRNA translational machinery by inhibiting cellular PABPC1 activity using different mechanisms. Picornaviruses, caliciviruses or lentiviruses encode proteases that cleave PABPC1 at several defined sites in the proline-rich linker region between RRMs and the C-terminal domain. Rotaviruses, gammherpesviruses and bunyamwera virus relocalize PABPC1 from the cytoplasm to the nucleus thus altering its function. Many of these viruses translate their mRNA in a PABPC1-independent manner and are unaffected by host PABPC1 inhibition. Belongs to the polyadenylate-binding protein type-1 family. Was termed (Ref.5) polyadenylate binding protein II.