Plays a role in translation initiation (PubMed:9624054). Translational GTPase that catalyzes the joining of the 40S and 60S subunits to form the 80S initiation complex with the initiator methionine-tRNA in the P-site base paired to the start codon (PubMed:12507428, PubMed:12471154, PubMed:12008673). GTP binding and hydrolysis induces conformational changes in the enzyme that renders it active for productive interactions with the ribosome (PubMed:25478828). The release of the enzyme after formation of the initiation complex is a prerequisite to form elongation-competent ribosomes (PubMed:12507428, PubMed:18976658, PubMed:19029250). Stimulates 20S pre-rRNA cleavage to mature 18S rRNA by PIN-domain endonuclease NOB1 (PubMed:22751017). GTP + H2O = GDP + H(+) + phosphate Binds 1 monovalent cation per monomer in the active site, which can be sodium or potassium. This structural cofactor stabilizes the GTP-bound 'on' state, and may also act as a transition state stabilizer of the hydrolysis reaction. Present with 13400 molecules/cell in log phase SD medium. Belongs to the TRAFAC class translation factor GTPase superfamily. Classic translation factor GTPase family. IF-2 subfamily.