ERF3b, or G1 to S phase transition 2, is a human gene encoded by GSPT2. It may also be known as: Eukaryotic peptide chain release factor GTP-binding subunit ERF3B; Eukaryotic peptide chain release factor subunit 3b; G1 to S phase transition protein 2 homolog. The encoded protein has an amino acid length of 628 and a mass of 68.9 kDa. Other isoforms may exist. ERF3b is a member of the TRAFAC class translation factor GTPase superfamily, Classic translation factor GTPase family, ERF3 subfamily. Homologs of this gene exist in other organisms, including: Mouse, Rat.