Involved in translation termination in response to the termination codons UAA, UAG and UGA (By similarity). Stimulates the activity of ETF1 (By similarity). Involved in regulation of mammalian cell growth (PubMed:2511002). Component of the transient SURF complex which recruits UPF1 to stalled ribosomes in the context of nonsense-mediated decay (NMD) of mRNAs containing premature stop codons (PubMed:24486019). Required for SHFL-mediated translation termination which inhibits programmed ribosomal frameshifting (-1PRF) of mRNA from viruses and cellular genes (PubMed:30682371). Component of the transient SURF (SMG1-UPF1-eRF1-eRF3) complex (PubMed:19417104). The ETF1-GSPT1 complex interacts with JMJD4 (PubMed:24486019). Interacts with PABPC1 (By similarity). Interacts with SHFL (PubMed:30682371). Belongs to the TRAFAC class translation factor GTPase superfamily. Classic translation factor GTPase family. ERF3 subfamily. eRF3 antibodies used in PubMed:19417104 do not differentiate between GSPT1/ERF3A and GSPT2/ERF3B.