As a subunit of eukaryotic initiation factor 2 (eIF-2), involved in the early steps of protein synthesis. In the presence of GTP, eIF-2 forms a ternary complex with initiator tRNA Met-tRNAi and then recruits the 40S ribosomal complex and initiation factors eIF-1, eIF-1A and eIF-3 to form the 43S pre-initiation complex (43S PIC), a step that determines the rate of protein translation. The 43S PIC binds to mRNA and scans downstream to the initiation codon, where it forms a 48S initiation complex by codon-anticodon base pairing. This leads to the displacement of eIF-1 to allow GTPase-activating protein (GAP) eIF-5-mediated hydrolysis of eIF2-bound GTP. Hydrolysis of GTP and release of Pi, which makes GTP hydrolysis irreversible, causes the release of the eIF-2-GDP binary complex from the 40S subunit, an event that is essential for the subsequent joining of the 60S ribosomal subunit to form an elongation-competent 80S ribosome. In order for eIF-2 to recycle and catalyze another round of initiation, the GDP bound to eIF-2 must be exchanged with GTP by way of a reaction catalyzed by GDP-GTP exchange factor (GEF) eIF-2B (By similarity). Along with its paralog on chromosome X, may contribute to spermatogenesis up to the round spermatid stage (PubMed:11528390, PubMed:25579647, PubMed:26823431). GTP + H2O = GDP + H(+) + phosphate The eukaryotic translation initiation factor 2 complex/eIF2 is a heterotrimer composed of an alpha subunit, also called subunit 1 (encoded by EIF2S1), a beta subunit, also called subunit 2 (encoded by EIF2S2) and a gamma subunit, also called subunit 3 (encoded by 2 homologous genes Eif2s3x and Eif2s3y). Widely expressed. In the adult brain, high levels in hippocampus, habenula, hypothalamic nuclei and cerebellum. Also expressed in embryonic brain. Knockout males are infertile. Their testes are smaller as compared to wild-type fertile males and exhibit spermatogonial proliferation block. Has a homolog on chromosome X (Eif2s3x). Belongs to the TRAFAC class translation factor GTPase superfamily. Classic translation factor GTPase family. EIF2G subfamily.