Eukaryotic initiation factors (eIF) are proteins involved in the initiation phase of eukaryotic translation. Eukaryotic translation initiation factor 3 binds to the ribosome subunit-mRNA complex. It has been implicated in preventing the large ribosomal subunit from binding the small subunit before it is ready to commence elongation.

PTK2 and EIF3S3 genes may be amplification targets at 8q23-q24 and are associated with large hepatocellular carcinomas. Amplification of the EIF3S3 gene is common in late-stage prostate cancer suggesting that it may be functionally involved in the progression of the disease. A recent study shows that eukaryotic translation initiation factor 3 subunit 3 does not seem to be over-represented independent of c-myc in prostate cancer [2][3][4].

In mammals, Eukaryotic translation initiation factor 3 is the largest scaffolding initiation factor, made up of 13 subunits (a-m). It is rough ~750 kDa and it controls the assembly of40S ribosomal subunit on mRNA that has a 5' cap or an IRES (Internal Ribosomal Entry Site). Eukaryotic translation initiation factor 3 uses the eIF4F complex or IRES from viruses to position the mRNA strand near the exit site of the 40S ribosome subunit, thus promoting the assembly of the pre-initiation complex [1].