IF5

IF5, or eukaryotic initiation factor 5 (eIF5), is a translation initiation factor found in eukaryotes and many archaea. It is a cytosolic protein that functions as a GTPase-activating protein for the eukaryotic initiation factor 2 (eIF2). In the context of the 43S pre-initiation complex, eIF5 stimulates GTP hydrolysis on eIF2 when the initiator tRNA recognizes the start codon, facilitating release of initiation factors and the joining of the 60S ribosomal subunit to form the 80S initiation complex. Through this activity, eIF5 contributes to start codon recognition fidelity and to the efficiency of translation initiation.

In humans and other organisms, EIF5 is the gene encoding this protein. It is broadly expressed and evolutionarily conserved. eIF5 interacts with other initiation factors such as eIF1, eIF3, and eIF2, and its activity is coordinated with the broader scanning and initiation machinery that governs protein synthesis. Regulation of EIF5 expression or function can influence global translation rates and is studied in contexts including development, cellular stress, and disease.

Note: The acronym IF5 can also appear in different scientific contexts to denote other entities; in molecular biology, however, IF5 most commonly refers to eIF5, the translation initiation factor responsible for promoting GTP hydrolysis during start codon recognition.