Nomenclature of Prokaryotic and Eukaryotic Initiation Factors
| Prokaryotes | Eukaryotes | Molecular Weight (form rabbit reticulocytes) | |
| Anderson (1975) nomenclature(1) | Ochoa (1976) nomemclature (2) | ||
| IF-1* | IF-MP | eIF-2** | 90,000 |
| IF-2** | IF-MI | eIF-2'** | 65,000 |
| IF-M2A | eIF-2a1*** | 125,000 | |
| IF-M2Bα | eIF-2a2*** | 16,000 | |
| IF-M2Bß | eIF-2a3*** | 19,500 | |
| IF-3*** | IF-M3 | eIF-3**** | 400,000 |