EIF5 is a critical component of the eukaryotic translation initiation machinery that functions as a GTPase-activating protein (GAP) within the 43S pre-initiation complex (PIC) 1. During translation initiation scanning, EIF5 interacts with EIF1 via its C-terminal domain (CTD) and with EIF1A via its N-terminal domain (NTD), maintaining the open PIC conformation 2. Upon start codon recognition, EIF5 promotes GTP hydrolysis by eIF2, and the resulting conformational change increases EIF5-CTD affinity for eIF2β, indirectly triggering EIF1 release and PIC closure 2. EIF5 then stabilizes the closed PIC conformation, preparing it for ribosomal subunit joining 2. EIF5 competes with EIF1A for binding to eIF5B with ~100-fold higher affinity, providing a mechanism to coordinate start codon selection with subunit joining 3. Recent single-molecule studies reveal that EIF5 binding is transient and concentration-dependent, dynamically competing with EIF1 to control translation start site fidelity 4. Beyond canonical initiation, EIF5 participates in IRES-dependent translation during viral infection and metabolic stress 5. CK2 phosphorylation enhances EIF5 affinity for both eIF2β and eIF1A, providing regulatory control 6. EIF5 dysregulation associates with hepatocellular carcinoma progression, suggesting clinical significance as a biomarker 7.