Acts as a coactivator in the regulation of translation initiation of poly(A)-containing mRNAs. Its stimulatory activity on translation is mediated via its action on PABPC1. Competes with PAIP2 for binding to PABPC1. Its association with EIF4A and PABPC1 may potentiate contacts between mRNA termini. May also be 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. (Microbial infection) Upon interaction with SARS coronavirus SARS-CoV NSP3 protein, plays an important role in viral protein synthesis. Interacts with the RRM1-RRM2 and C-terminus regions of PABPC1 in a 1:1 stoichiometry. Interacts with EIF4A. (Microbial infection) Interacts (via PAIP1M) with human SARS coronaviruses SARS-COV and SARS-COV-2 NSP3 protein (via SARS-unique domain); the interaction increases binding affinity with PABPC1. Only the PABPC1-interacting motif-1 (PAM1) stimulates translation initiation.