IF3

IF-3, or translation initiation factor 3, is a bacterial protein that plays a central role in the initiation phase of protein synthesis. It is typically encoded by the infC gene and is found across many bacteria and in organellar genomes such as those of mitochondria and chloroplasts, where homologous factors operate similarly.

IF-3 is a two-domain protein consisting of an N-terminal domain and a C-terminal domain linked by a flexible tether. The protein binds to the 30S ribosomal subunit, where it helps prevent premature joining of the 50S subunit and contributes to the proper assembly of the initiation complex with messenger RNA and the initiator tRNA.

During initiation, IF-3 promotes the formation of the 30S initiation complex by facilitating correct positioning of mRNA and formyl-methionyl-tRNA (fMet-tRNAi^Met) in the P site, and by enhancing start codon recognition. This activity improves the fidelity of initiation by reducing initiation at incorrect codons. After the 50S subunit joins to form the 70S initiation complex, IF-3 is released along with other initiation factors, allowing elongation to begin.

There is variation in IF-3 among bacterial species, including differences in domain length and surface features, but the two-domain architecture is conserved. The infC gene encoding IF-3 serves as a useful molecular marker in bacterial phylogenetics due to its evolutionary conservation.

Disruption of IF-3 function can impair translation initiation and cell growth, making IF-3 a subject of study in translation mechanisms and, in some contexts, a potential target for antimicrobial research. Its essentiality varies among organisms.