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. Its function in translational initiation regulation can either be enhanced by PAIP1 or repressed by PAIP2. 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. Involved in translationally coupled mRNA turnover. 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. 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. By binding to long poly(A) tails, may protect them from uridylation by ZCCHC6/ZCCHC11 and hence contribute to mRNA stability.
Subcellular locations: Cytoplasm, Cytoplasm, Stress granule, Nucleus, Cell projection, Lamellipodium
Localized in cytoplasmic mRNP granules containing untranslated mRNAs (By similarity). Shuttles between the cytoplasm and the nucleus (By similarity). During stress and in the absence of DDX3X, localizes to the nucleus (By similarity). At the leading edge of migrating fibroblasts, colocalizes with DDX3X (By similarity). Relocalizes to cytoplasmic stress granules upon cellular stress where it colocalizes with ENDOV (By similarity).