Type I IRES elements require a two step initiation process, in which the 40S subunit binds to the IRES and scans the mRNA for the AUG codon. Type II IRES elements contain an AUG codon near them, thereby not necessarily requiring direct contact with the 40S subunit. Rather, the 40S subunit is believed to be directed by bridging factors (Sachs et al., 1997).