SUI1 is a translation initiation factor that directs the ribosome to the translation start site, helped by eIF2 and the initiator Met-tRNA. SUI1 ensures that translation initiation commences from the correct start codon (usually AUG), by stabilizing the pre-initiation complex around the start codon. SUI1 promotes a high initiation fidelity for the AUG codon, discriminating against non-AUG codons.
In E. coli however, it seems that the SUI1 homolog YciH is an inhibitor of translation during stress instead.