IF-3 is thought to function as a fidelity factor during the assembly of the ternary initiation complex which consists of the 30S ribosomal subunit, the initiator tRNA and the messenger RNA.

[1] The chloroplast homolog enhances the poly(A,U,G)-dependent binding of the initiator tRNA to its ribosomal 30s subunits.

However, in E. coli, it is required for the 30S subunit to bind to the initiation site in mRNA.

It also allows for rapid codon-anticodon pairing for the initiator tRNA to bind quickly.

[4] Human mitochondria use a nuclear-encoded homolog MTIF3 for translation initiation.